Custom truck camper, let's talk materials

[Hillbilly Heaven]

If you use foam make sure you use Closed Cell Foam of whatever type you are using. Open Cell Foam will trap moisture and if you are using a steel structure will cause rust. Make sure any holes drilled into hollow structures are sealed. Holes allow moisture in. They do make closed end rivets and if you want to get fancy with your fasteners you can use closed end RivetNuts. I would apply sealant to all rivets.

If you want to fill tubing with foam after welding drill a hole top and bottom of the tube and fill with expanding foam. What little heat that would be required to spot weld the hole shut will not melt that much foam. Again make sure the expanding foam is a closed cell type foam. Would not hurt to spray undercoating inside the tube before the foam. Eastwood Restoration carries aerosol undercoating with a flexible tube to reach into hidden areas.

 

[aernan]

Ok can't take air post air box. I guess I need to find a smart location to pull in fresh air.

 

[freedrive]

Just FYI, one way to prevent rust inside metal tube frames...for decades steel frames of aircraft were filled with heated Linseed oil and drained. I think they use a product from LPS now, LPS #3 or such. These steel tube frames can sit outside in northeastern humid/cold/hot environment for a few decades before any major rust issues arise.

 

[aernan]

Voids in structures. Just thinking out loud here, but a hollow tube is an air gap, in a similar way to the air gap between window panes. Curious about the necessity to fill those voids.

With a tube steel frame, one could also weld eyelet lifts on top of the camper for overhead lifting. Not as much of a use for a camper back vs. say a medium duty truck big platform type habitat, but could be quite useful in the right situations.

http://www.smartrate.com.au/media/articles/demystifying-air-gaps

An air gap has an R value of 0.6 . If you stuff any kind of insulation in there you can get much better insulated values.

 

[s.e.charles]

Just FYI, one way to prevent rust inside metal tube frames...for decades steel frames of aircraft were filled with heated Linseed oil and drained. I think they use a product from LPS now, LPS #3 or such. These steel tube frames can sit outside in northeastern humid/cold/hot environment for a few decades before any major rust issues arise.

interesting. bicycle frame builders use "frame-saver" the same way. there are proprietary products available, but I have been known to use BoeShield T-9. just spray the livin' bejeepers into every hole in the frame using the long red straw, roll the frame around a bunch of times, and hang to drip over some newspapers.
sort of like this:

 

[freedrive]

^Haha!
I've also been known to spray T9 in and on anything metal that might be outside for a few months or more.

 

[DiploStrat]

You may be overthinking some of this. Hard to beat a pair of rooftop fans - one in/one out. I really like the thermostatically controlled Max Aire model.

My problem is that I have only one fan as I stuck an air conditioner in the place of the other one. I can keep smaller Seitz windows in the micro vent position, but I don't really get enough air into the camper when driving.

Finally, we have a solar powered vent in the bath. With any sunlight at all it runs 24/7.

Some thoughts for you to consider.

 

[tanuki.himself]

If you need to keep that much heat in have you thought about a heat exchanger? I've fitted a couple domestically which would probably be too large for a camper, but you might find something you can cut down or bodge. Basically they are a stack of conductive plates where hot air being sucked out passes on one side of the plates which transfer some of the heat to warm the incoming cold air being sucked in by another fan. They claim to recover upto about 75% of the heat, and it pulls the moisture out as well. Small space doesn't need big fans, and presumably you could also put a filter over the inlet fan and use it to provide positive pressure while driving......

https://fans4less.co.uk/heat-recove...ry-unit-low-cost-whole-house-ventilation.html

 

[freedrive]

So assuming 1"x1" or 1"x1.5" square steel tubing for frame, what thickness would you folks use, 16ga (~0.06"), 18ga (~0.05"), other?

I think I'll buy a small amount of steel, aluminum, rivets, etc and see how well a panel ;(with seams, edges, maybe a bend) turns out.

 

[freedrive]

Playing around with sheet aluminum alclad (0.032" thick), square steel frame, rivets.

 

[Hillbilly Heaven]

MMM maybe a problem putting aluminum on steel. Electrolytic action between two dissimilar metal will cause corrosion. You would at least be better off using an adhesive instead of direct metal to metal contact or contact thru the pop rivets.

 

[freedrive]

Good point, I do plan to put Sikaflex 221 between sheets and frame, which should give decent protection if I get good coverage. But then there's the rivets. They have aluminum head and steel shaft.

 

[Trestle]

1" x 1" vs 1" x 1.5" tubing - My understanding is that the strength of the tubing relates to tube size, and the durability relates to wall thickness. If going smaller, size up in wall thickness. I would rather go with the larger dimensional tubing with the thicker walls spaced further apart, but that is just instinct which of course may be wrong. I also find the thicker stuff easier to weld, but that may be just me.

Aluminum sheet on steel - The sikaflex should help with this (you could also use something like butyl tape as a standoff if not using sika, but then you need more fasteners as this would not provide the bonding action of the sika). If you could find some dimensionally thicker (say 1" wide by 1/8") tape that also provided a bond, that would be the best of both. Don't know of one, so if you find one share with us.

Rivets - I have worked a lot on an old airstream. Rivets will pop over time, or at least they do all the time on those types of trailers. You simply carry a kit, and repair them as "ongoing" maintenance. Trying to drill out a steel rivet from the surrounding soft aluminum sheet is problematic at best. The steel shaft parts never break off strait, so a punch doesn't help much to keep the bit centered. Much easier when the whole thing is of similar material. I would use larger diameter aluminum rivets (say 3/16) instead of the smaller aluminum steel rivets. Use the Sika on the rivets when setting so that the shaft and everything just below the head is coated. This provides some protection between the steel tubing and aluminum rivet sleeves, as well as helps to seal each hole.

Aluminum sheet - The alclad (2024T3) is great for polishing. For corrosion resistance and formability they used 5052 on the bellies of old airsteams. I am sure both are fine, but something to put in the memory banks for other projects. If the project skin will be painted, it does seem like you could save the extra cost of Alclad with another type of aluminum.

 

[aernan]

1" x 1" vs 1" x 1.5" tubing - My understanding is that the strength of the tubing relates to tube size, and the durability relates to wall thickness. If going smaller, size up in wall thickness. I would rather go with the larger dimensional tubing with the thicker walls spaced further apart, but that is just instinct which of course may be wrong. I also find the thicker stuff easier to weld, but that may be just me.

You can look up the deflection values for any type of tubing. In residential construction the max allowable deflection is 1/4". It's designed that way to avoid tearing the paper on the face of drywall under flex.

The strength of the tubing is a combination of wall thickness and diameter. It is also very directional. Imagine how floor joists are tall and narrow because the flex is all in the up down and not side to side.

Given the choice of using 5 (big) vs 10 (smaller) joists the higher joist count distributes the load more evenly but you will get more thermal bridging. Figuring this stuff out is pretty simple with math.

The durability of the tubing is related to how much flex you put it under and how ductile the material is. If you overbuild then there will be essentially no flex and the material will only fail on corrosion. If you build too light you will get flex and that can cause stress that makes the material fail. Most steel can flex and return to original shape for a long time. Aluminum will "work harden" and eventually crack. Some aluminum is very ductile and can survive frequent flexing. We all intuitively know this. Bend a paperclip back and forth till it breaks and try the same thing with some copper house wire or bailing wire. Materials designed to be ductile are soft and will deform but you can flex them a lot before they break.

 

[Trestle]

Yes all calculable with a bit of research and math for sure. I am more in concept at this point. Larger tubing further apart vs smaller tubing closer together is in my mind similar to building a house with 2x6 at 24" vs. 2x4 at 16". More insulation, less thermal bridging, and the like. As to steel vs. aluminum tubing I am still in the steel camp for the structure. Yes it will weigh more. The significantly larger flex cycles in steel (obviously thickness/dimension/and other factors affect this) vs. aluminum, the fact that it is easier to get repaired with a low skillset if needed, and slightly lower thermal capacity as compared to aluminum all weigh in on that preference. Aluminum skin vs. steel is less of an issue in my mind so long as you deal with bonding two dissimilar materials if going the aluminum route. Someone who has engineering skills could optimize it such that the skin would provide reinforcement to the structure, so that exotic materials are not necessary, and the weight does not get out of hand. For the rest of us, it is trial and error. Hopefully someone else's error that one an learn from rather than repeating mistakes that other have already made and learned from. That's the beauty of forums like this, though they are only as good as what is contributed. I hope to try some concepts, and to be able to share them over time. Most of this has likely been dialed in, but it is not necessarily fair for us to ask people who make their bread and butter off of having figured these things out to share the secret sauce.

The important thing to note is that every combination will have its place. When you take into account the tools/skillset/material availability/intended purpose/budget/platform/weight/temperature range requirements/etc. each category will push up and down on a sliding scale until you can come up with the appropriate combination. Otherwise we may all end up with a honeycomb formed structure made out of kevlar/carbon fibre skin with built in sound/temperature isolation, a structure that is so damn strong it could (intentionally or otherwise) stiffen the frame of the carrier vehicle, have nearly unlimited fatigue cycles, and weigh next to nothing in the process. Unfortunately that pesky budget might get in the way a bit.