Truck camper build proposal using pre-fab PU/FRP sandwich panels

[GuestArtist]

Greetings EP members, I'm an enthusiastic reader of this forum and mechanically-inclined neophyte with RV building.

I recently acquired sandwich panels which are cut-outs used in the manufacture of garage doors. Each panel is either 20"W or 22"W, with 80"L and having a thickness of 1.75". The distributor of these panels markets them as insulated wall coverings for shop and farm use, but they seem like a great material for an RV. Given the very inexpensive price being charged, the purchase of these panels was a no-brainer given their almost perfect dimensions for the build of a slide-in truck camper I've been pondering.

Though I figured it might be a challenge to join the narrow panels into larger watertight assemblies, my long road trip to the distributor's location gave me plenty of time to appreciate how much more effort I'd have to expend attempting to wrap my own panels from XPS which likely wouldn't result in nearly as good quality as these.

I discovered these panels are composed of a ~2 lb. PU insulation core and faced on both sides with a white gel-finish FRP sheet, having an estimated weight of perhaps 20-23 lbs.

The proposed project can be described as a truck camper with no cabover, having overall dimensions of 76"L x 66"W x 66"H with a 40" wide floor. I'm hoping to achieve a sub-400 lb. unloaded weight. While these parameters should easily support mounting in the bed of a mid-sized truck, initially I'm thinking to secure it to a 4x6 trailer.

The construction method I'd utilize is butt-jointed panels supported with angle brackets bonded on the exterior and interior corner joints, with perhaps a series of rivets for facilitating placement of these angles.

For the roof assembly I'd join three 22" panels along the long edges, aligned and reinforced with shallow splines inserted and epoxied behind each face perhaps 2" on either side of the joined edges. Further reinforcement of the entire assembly might come from tubing embedded inside the perimeter. Being a horizontal surface exposed to constant elements, it would probably be wise to glue an additional FRP layer to the exterior face to seal the joints, instead of relying on a fileted epoxy joint or sealing strip as I may attempt to incorporate on the vertical surfaces.

I'm hoping that the experienced amongst you can (in)validate my proposed approach and make comments that are not just limited to...
-- where/how to install lifting points (alternatively could the unit be somehow winched/dragged/rolled onto a truck bed instead of lifting)
-- necessity for reinforcing of panels/assemblies with embedded tubing or other
-- suppliers of angle/corner hardware (eg where to find FRP angle less than 1/4" thick) and compatible adhesives that are available in the USA
-- method for reducing the height of a standard RV door assembly for adaption here

Construction will be taking place in a residential-sized garage bay which is partially heated and can be supplemented with temporary additional heat.

Thanks to all for your prior contributions and I look forward to the comments.

 

[simple]

Seaming the panels together kind of seams like broken surfboard repair.

What climate are you planning to use the camper in? If you're in the SW, you might get away with joining them via an H aluminum extrusion. If you can't find that profile, you might be able to rivet and epoxy 2 C extrusions together to make an H extrusion.

You might also consider welding out an aluminum exo frame and bonding the panels to the inside of it.

Another method would be to fit them together and lay fiberglass over the seams.

 

[rruff]

Thoroughly test whatever methods you may want to try. I'd start with what I think would be best/easiest, which is to epoxy-fiberglass the joints. Start by butt joining and gluing the two pieces together, then wet-lay over the joints. You can buy woven "tape" in different widths and thicknesses. You'll need to sand the FRP well.

Don't know of any FRP angle <1/4". Thinner aluminum is common though.

Brophy cable jacks do not require lift points, but you will need the sides of your camper to stick out little farther than your truck/wheels.

If you want a short door, they are readily available. Try teardrop doors.

 

[plh]

4' x 6' is utterly small --> go at least 5' x 8'

 

[Shawn686]

Don't forget about thermal transfer if you go with metal connections. You may get condensation at all the joints depending on the temperature differential between in and out.

Shawn

 

[Pntyrmvr]

Take a look at how SIP panels are splined together using a 2x4 for some theory ideas.

You do know they make tube 2x2 and 2x3s in fiberglass...

 

[Alloy]

Suggest you look into the way freezer/cooler boxes are put together.

I took a 30,000sqft freeze box down that used a light aluminum T with a 3" top and 1 1/2" leg. Holding the inside/outside aluminum T together was 1/16" FRP riveted to the aluminum. It worked pretty good because the inside temp of the freezer was 0F with no condensation on the outside aluminum.

 

[GuestArtist]

OP here... thank you for your affirmations and creative ideas.

I believe there is/was an Australian member who produced detailed videos building expedition bodies using from steel-faced freezer or 'coldstore' panels. It was from these that I gained some hope that it a small RV body could be built by sectioning panels together.

My target use for this is as a tent replacement used mostly for mild-weather road touring and the occasional light off-road venture. I am based in the NE US so thermal bridging is a thing, but not a huge thing given the size and use case - nonetheless I shall seek to avoid it in my build.

While the idea of a welded exoskeleton is appealing, I cannot DIY that work and am convinced that using only adhesives for joining is feasible. I perceive that glued exterior and interior angles will act as a clamp for the whole shebang in a similar way to an exo-frame, though it may turn out that the spliced panels will compromise the strength so as to require one. Depending on test results, an alternate plan for these panels is to utilize them as sheathing for a small travel trailer, which could be constructed around a structural frame that supports VHB-taped panels.

Here's a picture of the splicing method I'd like to attempt. I envision using a hot-cutter to create the voids for FRP bar splines of perhaps 1/4", and simply epoxying them in... seems like it'd be plenty strong:

 

[GuestArtist]

Will be ordering some Sika 252 or Koemmerling Korapop 225 (recommended by the Total Composites folks) for some test panels - more to come.

 

[mog]

You might want to check out Dan Grec's (The Road Chose Me) new video on YouTube as they bond two panels together to make the roof panels.

 

[GuestArtist]

Thank you for posting the Dan Grec video, the splicing method he's using seems to work well with those honeycomb panels. In my case this approach might be superior to gluing in solid reinforcing material if I could formulate a compatible filler mix for the PU core... an interesting technique for sure.