Composite camper - aluminum extrusion vs. FRP edges

[MikeSkril]

I'm in the early stages of planning a small DIY flatbed pop-up camper for a Tacoma.
I started looking at composite, then checked out aluminum constructions, self-made fiberglass, and everything in between....just to come back to composite. I'm a metal guy, so it took me a while to swallow this...but I think composite is just the best option.

At the moment, I'm reflecting on how to join the composite panels. I'm aware of the concerns and possible drawbacks of aluminum in this construction but there are a few practical advantages. I have these 2 possibilities on the table. 'A' is much easier to work with and not very costly. 'B' might be better because panels and FRP will contract/expand the same way and have less thermal transfer, but it will be more work and cost more. Companies have been building campers and commercial vehicles using method 'A' (without the XPS corner) for many years and it seems to work well.

Has anybody used either of these methods? Any other ideas? There might be other options available, but this is what is available to me (Canada)
...or maybe I'm missing other options?

 

[Louisd75]

I would prefer method B but with a lap joint instead of a miter joint. Method A will work but I would worry about condensation in the corners.

 

[MikeSkril]

It would seem that A would have a cold bridge in the corner. And I agree with @Louisd75 that a B lap joint would be better and easier to assemble.

For reference, this is the way Total Composite joins its corners with a special fiberglass extrusion
View attachment 795440
FYI - They DO NOT sell just the extrusions, only complete kits through their TC approved builders

Globe Trekker LLC in the PNW uses aluminum extrusions (again special, not OTC) with a similar overlapping design. (The finger is pointing to a thermal bridge they install into the aluminum).

View attachment 795441

Yeah I'm aware of TC...I cannot get it for a DIY project. :-(

 

[Victorian]

It would seem that A would have a cold bridge in the corner. And I agree with @Louisd75 that a B lap joint would be better and easier to assemble.

For reference, this is the way Total Composite joins its corners with a special fiberglass extrusion
View attachment 795440
FYI - They DO NOT sell just the extrusions, only complete kits through their TC approved builders

Globe Trekker LLC in the PNW uses aluminum extrusions (again special, not OTC) with a similar overlapping design. (The finger is pointing to a thermal bridge they install into the aluminum).

View attachment 795441

I agree that the miter joint is a potential weak point. Nothing wrong with butt joints and capping everything with a FRP angle all around. That's how most expo trucks in Europe are build.

Here is a video of our current construction method.
watch

 

[MikeSkril]

I agree that the miter joint is a potential weak point. Nothing wrong with butt joints and capping everything with a FRP angle all around. That's how most expo trucks in Europe are build.

Here is a video of our current construction method.
watch

Good to know, thanks! ...I'm having trouble so far finding a suitable FRP angle.

 

[dstefan]

One aspect of Option A to consider is aerodynamics. A huge amount of our fuel inefficiency is due to the drag of the big boxes on the back of our trucks on the highway. As fuel costs continue to go higher they may be a bigger detriment to getting out there than some minor thermal bridging. What’s that got to do with joining composite corners?

Here’s what NASA’s truck research shows (no, not a typo): "Rounding all four front edges yielded a 52-percent drag reduction, while sealing the bottom of the vehicle gained another 7 percent. The engineers estimated the potential gain in fuel economy to be between 15 and 25 percent at highway speeds.” https://spinoff.nasa.gov/Spinoff2008/t_3.html

Those four or more hard angle corners on our campers are real expensive over time.

I have zero composite camper experience . . . just so you know, but I also sure get the concerns with thermal bridging having an aluminum camper with plenty of it. Fortunately I live in the desert!

Just one more variable to drive you nuts in your design process! 🤔

BTW, I’m looking for lightweight rounded corners to retro fit on my camper. Anybody have a source? Haven’t really found anything yet.

 

[dstefan]

I can see why you came to that conclusion, but the streamlining shown in that image is addressed later regarding the front of the cab. There’s a far more detailed many page PDF of their research I’m struggling to find, but have read in the recent past. They started with a perfectly square box then radiused the corners. Not sure of the size of the radius, but I’ve seen a picture of it and it’s pretty similar to what bigger campers have. I believe the section I quoted above is in regard to that.

I’m not trying to claim that anyone would get some huge benefit from radiused corners, but just saying that the aerodynamics come into play. How much? Who really knows without wind tunnel tests. Just something to consider.

 

[dstefan]

This was the van they started with and rounded the edges first to get their intital results. A boxy camper on a truck would see less result certainly because you’re starting with a more streamlined shape given the nose of the truck and the windshield rake, but it can still be a considerable drag reduction depending on the “box”.

 

[dstefan]

Ahhh … I bow to your superior GoogleFu …well found!

 

[MikeSkril]

@dstefan @mog Man! You are hijacking my post with your aerodynamics.

 

[dstefan]

My bad! All done …😔

 

[jwiereng]

What is your Canadian source of the corner extrusions?

 

[MikeSkril]

What is your Canadian source of the corner extrusions?

I have not found a good source so far... :-(

 

[Victorian]

I have not found a good source so far... :-(

Simple 3mm thick FRP L profiles are common in Europe. Anything else is most likely unique to each manufacturer. Our FRP pultrusions are made specifically for us.

 

[jwiereng]

I have not found a good source so far... :-(

Ok, Your first post say "Has anybody used either of these methods? Any other ideas? There might be other options available, but this is what is available to me (Canada)"

It made me hopeful that such a thing was available in Canada for self builders. I also live in Canada. Please keep us posted if you find a suitable product