DIY trailer build

Cramshire

New member
Hello! This is my first post here, and I'm not entirely sure how best to organize this. In April 2024, I really wanted to build a camp trailer for our family of 4, and had (misguided?) ideas of it being off-road capable. What I ended up with was a pretty great build for us, but there were definitely some compromises along the way.

Mainly, I just want to share my build experience with a community who thinks this kind of thing is interesting. So maybe I'll just start at the beginning..

I started with a bunch of hand drawings and then built some models in the basement out of 2X4's and plywood. I wanted to keep the total weight under 2500lb fully loaded, so this meant it had to be as small as possible, while still being comfortable. I also wanted to keep it under $20,000. Once I had a good idea of how I wanted it laid out, I started modeling it up in CAD. CAD is great, but it doesn't really do anything magic, you still need to know what you're going to make everything out of and what components you are going to use. It's actually a lot more work in the front end, but really amazing to have as the build comes together if you spend the time. Anyway, it was time to figure out what to build it out of.

I wanted to use fiberglass - foam sandwich panels with aluminum extruded corners that are thermally isolated. This was the hardest thing to source by far, I spent a lot of time on the phone with companies that didn't really want to talk to me. I finally was able to secure an actual quote for panels made in Canada, from an outfit called CPT "Composite Panel Technologies". They ended up working out, but it was a huge pain to get information out of them about the simplest questions, I was nervous a few times that they were never going to show up, but it ended up being fine if I called them enough! They actually included all the Sikaflex 252 I would need and some other nice details in the end.

Now that I had the main building material chosen, I started researching the actual trailer. I had it in my mind that I wanted it to be aluminum for weight savings, but after talking to a lot of trailer builders, it seemed pretty clear that a steel trailer of this size was not really any more heavy, unless the aluminum trailer is built very carefully and heat treated after welding etc. I talked to a bunch of trailer builders, and finally chose someone to make the frame, but that fell apart in the end, they just were not able to get it done in time and didn't want to do anything custom. At this point I decided to weld up my own trailer, using Timbren suspension (which I don't love now that I have it).

With the trailer and camper material chosen, I was able to refine the CAD. I modeled every detail I could, including the Timbren 3500 axle-less suspension and all the other trailer parts. I chose a battery system (more on that later), a fridge, an AC, a heater, propane tank mounts, sink and water system, composting toilet, stovetop, windows, and door among other things. With all this modeled and looking good I started building!

cad.jpg

The above is the Solidworks model. I ended up with Arctic Tern Door and Windows which have been really awesome, although the cost is a bit insane. The lights and trailer hardware / fenders are from e-trailers, and the fridge/stovetop are dometic. I don't have solar on there yet, but they will be Rich Solar MEGA 250 panels I think.

The general layout can be seen in the CAD, there are 2 benches with storage underneath, and a large table that seats 4 average size people easily. I really wanted a spacious place to hang out and play cards with the 4 of us, and it was a bit tough to fit in there. the total outside dims are 10'6" X 6'.

The table is held down with magnets, this works way better than I thought it would! It lays down to complete the center bed, and one kid goes up in the bunk, and one kid goes under with the dog ;-). Maybe not the best arrangement for 4 adults, but pretty fine for a couple of teens.

Here are some images of parts when they arrived at my house. Poor UPS guy....

- (374).jpg

This is all the steel for the frame in the shop!
- (391).jpg

8X 230ah Lifepo4 cells for the battery

- (418).jpg

All the panels, glue, and corners before I cut them

- (352).jpg


That is probably enough information in one post? I don't have a huge number of photos of the build process, but a few and I'll follow up with more on the build if people are interested.

Thanks for having a look!
 

Cramshire

New member
Thanks all for checking out this post! I found some time to add a bit more.

Once the frame materials came in I started cutting and welding. I have a pretty big shop for work, with a nice horizontal bandsaw and some good welders, it was very nice to be able to use it for this. The frame went together really well, I used 2X3 X .120 rectangular tubing and some 1.5 X 3/16 angle. I strengthened the Timbern mount points with 1/4X4 angle, and used the 2X2X.25 tube to go between the "axles" as recommended by Timbren.

I really took my time with this, and capped off all the tube ends and ground everything to a nice smooth finish where it wasn't structural.

frame welding 3.jpgframe welding 2.jpgframe welding1.jpg

In the below image you can see the leveling jacks, and if you look closely the Timberen axles. They are the standard duty 3500lb axles with no drop. These were an absolute nightmare to align, I don't think I would use this setup again just from an alignment aspect. Also, the supplied bolts were junk, they stretched and never got tight way before reaching the specified torque using a quality torque wrench. All of the alignment (camber and tow) depends on 4 half inch bolts in a small pattern at the end of the axle forging. There are no alignment features, it just depends on friction, with shims to tweak camber. As an engineer it just makes me cringe! Once I got the thing "aligned" I tacked the axle forgings to the pivot arms, just so there was at least something besides these bolts keeping the wheels pointed in the right direction.

Timbren on and aligned.jpg

The trailer frame is designed with a 2 1/2in lip all the way around that is 3X.120 flat bar welded all around. This way the floor panel glues to the frame cross bars and the walls come down all the way to the top of the rectangular tubing. There is a full 2.5in of glue surface on that lip, all the way around, and then there is angle aluminum inside securing the floor panel to the walls. Ill post some pictures of that.

Here I am cutting out the panels. This actually was not bad, I was a bit worried about it. I used a cordless skill saw with a carbide fine tooth blade and it was quite easy. I'd recommend a respirator, tyvek suit, gloves etc. Fiberglass is lovely stuff. My biggest regret here was that I knelt on the wall panels (they are a little thinner than the roof and floor) and it put small dents in the panel. No one else will ever notice, but still... Overall I was happy with the panels, they are quite strong, but I would not say overkill. They were 1.5in XPS foam with 1.5mm (walls) and 2mm (floor and ceiling) fiberglass skins. Some folks told me the XPS was going to be terrible and squishy, but I found it fine. You can walk around on the roof and it hardly flexes, and I have no concerns about the Arctic Tern compression seal windows crushing it.

panel cutting.jpg

I used Sikaflex 252 with Sika 207 primer for bonding the panels. It was a bit of a process, I roughed up all surfaces with Scotch Brite, cleaned with water, and primed with the Sike 207. I made a couple of test joints, and this is strong stuff! The primer does help. One 8oz bottle did the whole project. I found it at McMaster Carr, they also have a good deal on Sika 252 if you need some.

Below I am gluing on the floor. You can see in this image that the frame is now black, I had it sandblasted and powdercoated. I hate painting, and wanted something very well bonded to the steel for the Sikaflex to bond to. This was a bit of a hassle, as you can see there are no fenders, I had to have them coated separately because the whole thing would not fit in their oven.

Floor glue 1.jpg

The triangles stuck in there are just to maintain spacing between the frame rim and the floor so the walls go in place right. This all went together pretty well! The glue is stiff, but a manual sausage pack caulk gun worked fine.

floor glue 2.jpgfloor glue 3.jpgfloor and wall glue 1.jpg- (340).jpg


More soon! Thanks all who are having a look.
 

Cramshire

New member
Did you say where you bought your panels? Sorry if I missed it.

Sent from my Pixel 9 Pro XL using Tapatalk
They were from CPT, Composite panel technologies, https://www.cptpanels.com/. I liked the panels that Boreas sells but they don't really have a corner solution. CPT has some nice aluminum extrusions for attaching corners. It was a bit of a hassle to figure out what was what but it worked out in the end.
 

ExpoMike

Well-known member
They were from CPT, Composite panel technologies, https://www.cptpanels.com/. I liked the panels that Boreas sells but they don't really have a corner solution. CPT has some nice aluminum extrusions for attaching corners. It was a bit of a hassle to figure out what was what but it worked out in the end.
Can you give a general pricing for these CPT panels? I love the idea of composite panels but cost has always been a big factor with them.
 

Cramshire

New member
Can you give a general pricing for these CPT panels? I love the idea of composite panels but cost has always been a big factor with them.
Sure. At the time (May 2024) it was about $15/square foot for the 1.5mm skins on 1.5in foam, and $16/sf for 2mm skins on 1.5in foam. The extrusions were $250 per 20' length, this included the inner corner and outer. This was the most expensive part. The scrap adds up too, because you are paying $15/sf for your window and door holes, and they only sell it in 8' widths, with 30' max length. It was about $7300, + $1000 freight for this little build (10.5'X6'X6')
 

Forum statistics

Threads
188,480
Messages
2,905,472
Members
230,494
Latest member
Sophia Lopez
Top