Custom truck camper, let's talk materials

[freedrive]

I keep coming back to a custom build. What to build it out of?

Goal: 8' slip-in truck camper, ~2 month build to a insulated shell with a few windows and a rear entry door, and easily modifiable to add very simple heat, a/c, cooking and electrical systems. (Think fancy backpacking style systems, not super luxo RV setup). I will probably design it so I can add pop-up in the future if so desired.

FRAMELESS:
Some sort of frameless composite: build time, picking the right material, and construction techniques, and hard to modify later, all seem to add up to too much for me and what I want.
So I quickly go to a metal frame.

FRAME:
Aluminum or steel (I can cut and weld either).

I just don't see a compelling reason to use aluminum, but I must be missing something because a lot of companies and folks use aluminum. I put together a comparison of a pretty substantial well-braced frame (total of 265' of tubing), and for example, got the following numbers:

1"x1"x0.083" steel square tubing, $570, 275lb.
1.5"x1.5"x1/8" 6063 square tubing, $1,300, 214lb.

I have a half dozen more comparisons (round, DOM, 6061), but from above what am I missing, steel seems like the obvious choice?

SIDING:
A common standard seems to be 0.090 sheet aluminum. Assuming a framed camper, is there a better choice? Should/could the inside be something else 'warmer' to the touch?

ATTACHMENT:
I've read some interesting things about 3M VHB adhesives. There are some amazing architectural uses of it (outside windows in buildings, etc).
See this test:
http://multimedia.3m.com/mws/media/...ctural-metal-panels-tb.pdf?fn=70070939676.pdf
I'm tempted. Anyone tried this or discounted it for a good reason?

Otherwise, glue, rivets, screws?

INSULATION:
I'm not too worried about extreme heat/cold. I may install A/C, but will install some sort of heat. I do want to control condensation.
Assume a 1" or 1.5" frame, good insulation choice?

In summary, it seems a steel frame, with VHB attached aluminum panels (outside) and maybe same or something else inside, would be easy to build, easy to repair, easy to modify, and fairly light weight.

 

[aernan]

After mulling over this for a long long time here are my thoughts.

Cheap RV are made from wooden frame construction with pink insulation and stapled on corrugated aluminum skin. It's cheap to construct and repairable. It is also very fragile and not very insulated.

Next step up they replace the cheap fir with hardwood to make the frame better. Still kinda fragile. May also have fiberglass skin. Also fragile.

Next step up they start doing the framing in steel. Excellent structure but kinda heavy. Can have decent insulation. Middle of the road for construction costs from what I have read.

Total Composites sells a composite made of fiberglass and foam and fiberglass or aluminum. It's awesome and can save hours of labor building the box. Then you are left to cut/fit windows and doors and assemble the corners with sikaflex and rivets. If you do got this route for box on frame you need a sub frame to avoid tortion destroying the box so you loose some vertical clearance. I believe this is fairly costly and not many providers of composites work with the public.

More modern RV are moving to welded together aluminum tubing because total weight is an issue when towing with mid size SUV. It's not ideal because aluminum tubing is costly and welded aluminum tends to warp like crazy. Joints are never annealed and there is lots of internal stresses. Still much better then any wood construction and lighter then steel.

I am going to opt for making beams from aluminum sheet. The beams will be riveted together and so will the final structure. This is how an airstream and airplanes are made. It's cheap tooling and very labor intensive but it's repairable. I will insulate using residential spray foam which has a very high R value. Since there will be no welding I can fill all the voids and avoid thermal bridging. The composite design is still better for insulation but "may" not be as strong. I can put beams and reinforcement wherever I want/need in the structure to hang furniture and make doors/windows strong. I will use sikaflex to glue the outer skin on to the ribs and then rivet at the edges. The riveted area will be covered in a cosmetic corner plate which hides the rivets and prevents water ingress. If I need to replace a panel I can de-rivet and peal it off and replace with like. (big labor but repairable)

Alternatively you could use the galivized steel beams used for residential construction. They are cheap and you can literally screw them together. Cutting involves tin snips.

I have a friend with sheet metal working tools so I can have the beams fabricated (bent) from stock and it ends up lower price then aluminum square tubing. The complex part was doing the engineering to make sure the floor would be strong enough. If you do opt for this method you should realize that the tooling is low cost but it is very labor intensive.

--------------------
Your questions.

Yes the 3m Tape products are great for attaching the skin.

Siding:
I'm doing aluminum inside and out with likely a fiberglass/plastic or furniture grade plywood interior on top. The aluminum will help as a structural element and the top layer is cosmetic.

Glue/rivet/screw
I plan on riveting. Any external rivet need to be blind and sealing so you don't get leaks into your structure. I would only screw if you were using the galvi beams. Screw heads are large. I'm planning on counter sinking the rivets for flush finish. There is a special counter sink drill bit that makes that possible.

Insulation:
I'm going to use residential spray foam with a target R value of 8. A vacum is 10 and so is carbon eurogel.
http://www.celblox.com/r-values-of-common-building-materials/
the pink insulation is 3.2 and the EPS/XPS from 4-6. I'm going to build my insulation layer to 2.3" which is on the thick side for cold weather. 1" even with good insulation would be a bit thin in my opinion. That puts my R at 8 * 2.3" = 18.4 for the walls. The windows will have a terrible value of something like 2 (dual pane). If you use the EPS at 4 and use only 1" you would have a R value of 4. Making my box 4.6 times more insulated.

Watch out for the power budget of an AC. Basically RV can only use the AC on shore power or when the generators are running because:
1. they take a lot of power
2. they have little insulation and lots of windows
3. the units they use are also inefficient

I'm planing my entire design around solar + DC inverter based AC unit + Lithium batteries (22kw). So I can cool my space. It's not hard to heat up the space with any type of heater.

 

[s.e.charles]

if weight is a consideration, why not spruce w/ marine plywood sheeting, and then your aluminum skin?

modification would require no more than a handsaw & block plane. wouldn't get much more simple than that.

check strength vs weight for spruce; it's right up near the top. like the biplanes, y'know?

http://www.hainesengineering.com/rhaines/misc/sitka.htm

 

[freedrive]

I keep thinking of, and forgetting about, wood. Having flown several planes with wood in them, it's a good choice.
FYI, I just need to manage weight, but it's not a major issue, it's going into an F250.

But, good point!

 

[s.e.charles]

yeahbut, … and i'm sure you have your reasons, a plane doesn't have a steel superstructure (does it?). the camper part is sort of independent of the vehicle. not likely you'll take the cockpit out of a plane, well, voluntarily anyway, but I believe some folks count on interchangability so either can be replaced without the other. i'll wager new bodies on military surplus, even tricked out military surplus, cost more than the truck. and then there is time and personalization, the "nesting" factor.

if your build timeframe is two months, and I assume that's working full time on it, you may want to consider sourcing materials as part of the efficiency coefficient to your decision. the "best" option often comes with a hidden penalty.

my previous employer had nice things, among which was an audi s8. except 'in the shoulders of the season' (I love that phrase) he had to watch the thermometer in the morning to see if he could drive it. apparently the tires were only at their peak performance above 40 degrees. so if we had a cool morning in October, he would need The Service to pick him up and bring him to "wherever."

worked for the guy for almost 10 years and I still don't know what he did when he "went to the office". checks never were late or underfunded, so I never really needed to know.

 

[freedrive]

After mulling over this for a long long time here are my thoughts.

Cheap RV are made from wooden frame construction with pink insulation and stapled on corrugated aluminum skin. It's cheap to construct and repairable. It is also very fragile and not very insulated.

Next step up they replace the cheap fir with hardwood to make the frame better. Still kinda fragile. May also have fiberglass skin. Also fragile.

Next step up they start doing the framing in steel. Excellent structure but kinda heavy. Can have decent insulation. Middle of the road for construction costs from what I have read.

Total Composites sells a composite made of fiberglass and foam and fiberglass or aluminum. It's awesome and can save hours of labor building the box. Then you are left to cut/fit windows and doors and assemble the corners with sikaflex and rivets. If you do got this route for box on frame you need a sub frame to avoid tortion destroying the box so you loose some vertical clearance. I believe this is fairly costly and not many providers of composites work with the public.

More modern RV are moving to welded together aluminum tubing because total weight is an issue when towing with mid size SUV. It's not ideal because aluminum tubing is costly and welded aluminum tends to warp like crazy. Joints are never annealed and there is lots of internal stresses. Still much better then any wood construction and lighter then steel.

I am going to opt for making beams from aluminum sheet. The beams will be riveted together and so will the final structure. This is how an airstream and airplanes are made. It's cheap tooling and very labor intensive but it's repairable. I will insulate using residential spray foam which has a very high R value. Since there will be no welding I can fill all the voids and avoid thermal bridging. The composite design is still better for insulation but "may" not be as strong. I can put beams and reinforcement wherever I want/need in the structure to hang furniture and make doors/windows strong. I will use sikaflex to glue the outer skin on to the ribs and then rivet at the edges. The riveted area will be covered in a cosmetic corner plate which hides the rivets and prevents water ingress. If I need to replace a panel I can de-rivet and peal it off and replace with like. (big labor but repairable)

Alternatively you could use the galivized steel beams used for residential construction. They are cheap and you can literally screw them together. Cutting involves tin snips.

I have a friend with sheet metal working tools so I can have the beams fabricated (bent) from stock and it ends up lower price then aluminum square tubing. The complex part was doing the engineering to make sure the floor would be strong enough. If you do opt for this method you should realize that the tooling is low cost but it is very labor intensive.

--------------------
Your questions.

Yes the 3m Tape products are great for attaching the skin.

Siding:
I'm doing aluminum inside and out with likely a fiberglass/plastic or furniture grade plywood interior on top. The aluminum will help as a structural element and the top layer is cosmetic.

Glue/rivet/screw
I plan on riveting. Any external rivet need to be blind and sealing so you don't get leaks into your structure. I would only screw if you were using the galvi beams. Screw heads are large. I'm planning on counter sinking the rivets for flush finish. There is a special counter sink drill bit that makes that possible.

Insulation:
I'm going to use residential spray foam with a target R value of 8. A vacum is 10 and so is carbon eurogel.
http://www.celblox.com/r-values-of-common-building-materials/
the pink insulation is 3.2 and the EPS/XPS from 4-6. I'm going to build my insulation layer to 2.3" which is on the thick side for cold weather. 1" even with good insulation would be a bit thin in my opinion. That puts my R at 8 * 2.3" = 18.4 for the walls. The windows will have a terrible value of something like 2 (dual pane). If you use the EPS at 4 and use only 1" you would have a R value of 4. Making my box 4.6 times more insulated.

Watch out for the power budget of an AC. Basically RV can only use the AC on shore power or when the generators are running because:
1. they take a lot of power
2. they have little insulation and lots of windows
3. the units they use are also inefficient

I'm planing my entire design around solar + DC inverter based AC unit + Lithium batteries (22kw). So I can cool my space. It's not hard to heat up the space with any type of heater.

Thank you very much for the informative response, excellent!

 

[downhill]

A properly designed aluminum structure should match the strength and resilience of steel at no more than 50% of the weight of steel. Usually people way over build aluminum to gain strength at the joints. Take a look at aluminum framed bicycles, and you will see that the tubes are very light, and the strength focus is on the joints. There is no point in using aluminum unless the design of the structure is appropriate to the material. People also make decisions about dimensions in materials for reasons other than strength, for instance choosing 2" tube so that you can use 2" insulation. A better choice for that wall might be formed channel rather than tube. Very strong and light structures can be built from many common materials, but the weight budget usually gets blown in the joining of the materials.

 

[brp]

Have you checked out Monopan or similar? To get all of your "system" in one layer (frame, interior, exterior and maybe insulation) just seems so slick.

You'd have very few penetrations, it would be very light, moisture/rot/rust proof, so many advantages. It is also very repairable.

It seems like you could build it very fast as well, perhaps have all the sheets cut in a day.

The stuff is expensive, but when factoring in everything, including your time, I bet it is a good value in the end compared to a more traditional frame/skin type of construction.

 

[aernan]

I've never worked with fiberglass or composits before. I have welded and done wooden structures before. Also I'm learning structural engineering right now to design my structures. So I'm going to steer clear of composites until I get some experience with them.

 

[freedrive]

Have you checked out Monopan or similar? To get all of your "system" in one layer (frame, interior, exterior and maybe insulation) just seems so slick.

You'd have very few penetrations, it would be very light, moisture/rot/rust proof, so many advantages. It is also very repairable.

It seems like you could build it very fast as well, perhaps have all the sheets cut in a day.

The stuff is expensive, but when factoring in everything, including your time, I bet it is a good value in the end compared to a more traditional frame/skin type of construction.

Monopan looks pretty interesting. Can heat and bend to get a radius, can rivit/screw/glue to it. Finding pricing is difficult.
EDIT: Thermal properties don't look good. So might need to add a measureable thickness layer of insulation.

 

[aernan]

If you want high performance insulation look for aerogel. You can buy it in 1/4" thick fabric sheets on ebay by the square foot. 1" is R10. You could add as many layers as needed to get your thermal properties you like.

 

[TernOverland]

With regard to insulation, pay special attention to cold bridging through glass and metal structures, and to how you handle air exchange. The actual R value of the walls is a far smaller contributor to overall thermal efficiency than some might think. A small living space like a camper does not have the same dynamics as a house. In a house, a very small percentage of the interior air must be exchanged in any given time to maintain a livable environment. In a camper that exchange is a relatively huge percentage. The two primary sources of heat loss for campers in cold environments are cold bridging and thermal loss due to air exchange. I have heard people make the argument that a camper is like a cooler, i.e., a better insulated cooler like a Yeti will perform better than a cheapo cooler. A better analogy is comparing those two coolers with the lid cracked for ventilation. In that case, the difference between them is much smaller. A camper is like a cooler with the lid cracked because unlike bottles of beer, we must breath and we must exhaust the moisture generated by our breathing and perspiration. My experience with insulation in small to medium sized campers suggests that the practical limit of the wall material R-value is around 7-8. The larger the camper volume, the more it will benefit from larger R values.

 

[Hillbilly Heaven]

So you are saying there should be some air leakage and not as tightly as a house. Although you lose thermal efficiency you gain air exchange unlike thermal bridging that has no air exchange. No vapor barrier?
What about using a small dehumidifier especially if you use propane to heat and cook?

 

[TernOverland]

If you want high performance insulation look for aerogel. You can buy it in 1/4" thick fabric sheets on ebay by the square foot. 1" is R10. You could add as many layers as needed to get your thermal properties you like.

Thanks for sharing this. I think there are a number of Aerogel products. Which are you familiar with? I'd like to investigate this further.

 

[TernOverland]

So you are saying there should be some air leakage and not as tightly as a house. Although you lose thermal efficiency you gain air exchange unlike thermal bridging that has no air exchange. No vapor barrier?
What about using a small dehumidifier especially if you use propane to heat and cook?

Yes, you must have air exchange in a camper. Otherwise the oxygen level would plummet, and the humidity would skyrocket. A dehumidifier would help with the moisture, but requires power, so again a trade off. By-products of combustion must still be exhausted. The issue with air exchange is managing it. Most people err way too far to the excess side, and throw away thermal efficiency for nothing. I'm actually in the process of building a test system to measure environmental markers like O2 concentration, hydrocarbon levels (un-burned fuel byproducts), Carbon monoxide (combustion by-product), moisture levels, and temperature. This system will allow me to tune air exchange in my personal camper so that environmental needs are met with minimal heat loss. My calculations suggest that huge gains may be made this way. The benefits are reduced fuel needs and a healthier living space.

Air exchange at least has some redeeming value, but cold bridging has none. Cold bridging is pure waste.