I would think for that type of design, you'd build the box around the tent?
Is this the type of design you're after?

- A friend of mine now owns this one (above), but I don't see the advantage to having to store your tent in a trailer when it fits in a cabinet by itself.
- WW Tent Trailer.png (153.86 KiB) Viewed 403 times

- This one is pretty cool, but the trailer doesn't have room for much of your galley/mess items once that tent gets in there.
- 1946 higgins.jpg (52.76 KiB) Viewed 403 times

- JC Higgins tent trailer.png (116.67 KiB) Viewed 403 times
I'm a big fan of canvas, just for the old-tymey factor, I've go two big canvas tents that I use regularly. A fold-up hard wall as Slow suggests sounds interesting. You would definitely need stabilizer jacks to keep it from rocking too much no matter what.