Can you describe exactly what you are talking about? ...
Some years back I was considering how to build a frame so that 2" rigid board XPS would neatly fit between frame skins allowing for some adhesive. Although I could have ripped lumber, I realized that I could also slice 3/4" (nominal) sheets of plywood in to 2" strips, and that 3 of those strips, glued flat together, would work quite nicely. (Although if 3/4" (nominal) plywood gets much thinner, that won't work anymore.
)
Although my design was for flat floor, roof, and walls (except for an angled wind-deflector at the front of the cab-over), curved structures could be made with thinner plywood strips glued together, as I suspect you are well aware.
Please keep in mind that I will describe building a box to help facilitate readers understanding of the framework and overlapping plywood, rather than for exact directions to build a camper.
For simplicity, let us consider a box with outside dimensions of 8' long, 4' wide, and 4' high. Skin thickness will affect plywood strip lengths if one wants to maintain the outside dimensions, so let us consider skins of 0" thickness.
For the 8' x 4' floor, start with (2) 8' strips placed 3'8" apart. Place (7) 3'8" strips between them. (2) at each end (forming a rectangle), (1) in the very middle, and (2) strips spaced between the middle strip and outer strips (on each side of the middle strip).
Glue (and clamp however one likes) (7) 4' strips across the 8' strips and the 3'8" strips.
Glue (12) (cut to length) strips between the gaps on each 8' length (6 strips per side).
Glue (2) 8' strips to the floor frame (1 on each side).
Glue (7) 3'8" strips to finish the "joists" of the floor "ladder" frame.
Skin both sides of the floor remembering to include the foam.
Build the long wall frames, keeping in mind that the long wall frame only needs to be 3'8" high (because the floor plus roof and 0" skins will make up the rest of the 4' height).
Build the short walls frames, keeping in mind that short wall frame only needs to be 3'8" high (because the floor plus roof and 0" skins will make up the rest of the 4' height), and the short wall frame only needs to be 3'8" wide (because the long walls and 0" skins will make up the rest of the 4').
Skin the inside of the wall long frames and the inside of the short wall frames (only the insides).
Glue the long wall frames to the floor skin.
Glue the short wall frames to the floor skin and to the long wall frame (interior) skins.
Make a roof by duplicating the floor.
Glue the roof to the top of the long wall frames and short wall frames.
Foam and skin (the outsides) of the long wall frames and short wall frames. Make sure that the outside wall skins overlap on the roof frame and on the floor frame.
......................................................
For additional strength (and work
), use scarf joints instead of butt joints.
For extra additional strength (and work
), cut some of the 8' "strips" with "nubs" for 2 (of the 3) layers of each 8' frame length. Cut them with 3" nubs and also with 6" nubs. Doing so offsets the joints. so that 2 butt joints (or scarf joints) aren't overlapping.
Yes, cutting "strips with nubs" from plywood would require additional work and material,
but hey, aren't all camper frames designed to work as roll-cages? ...
....................................................
Skins have thickness in real life. Remember to include them while designing a box (camper).
To help with shedding water, I suggest designing the box (camper) so that the top roof skins overhangs the underneath outside wall skins. I also suggest designing the outside wall skins so that they hang down to the bottom of the bottom floor skin.
