Get one of the old Military trailers.  We used to have a few of them at our scout camp. We got them for free for the military along with a few 1978 Dodge Power Wagons.  We used one for garbage and one had racks on it to move boats or something.  I remember they had a pintle hook connection and lots of clearance.  I actually flipped the garbage trailer.  Luckily it was empty at the time.  The carb was messed up on the Power Wagon and it took off right when one tire went in a hole and the other hit a rock.  I have seen these trailers often and many variations of things done to them.  I think they are about 6x6 box.

On the other hand, You could just get an enclosed trailer.  It has been about 15 years since I was driving around our camp but most of the roads were driveable in a 2wd vehicle with moderate clearance and sensible driving.  A small enclosed trailer would work.

On the other hand, I often remember some camps didn't let you drive past the parking lot even on the semi main road (our camp wasn't like that and many of us volunteered on the weekends and had access to camp vehicles).  I understand not letting people on the fire roads but these were just dirt roads.  One of the camps wanted us to pay $15 to load it in the rangers truck and for him to drive it in.....meanwhile the stuff was already in a 4X4 pickup.

Interesting project.  I would probably start with a pre-built trailer frame and go from there.  Something like this:

http://www.harborfreight.com/1.....94564.html

What I would do is build a box for the cargo area, just taller than your chuck box (say about 18" high) with a platform over the top and a fairly large door at the back.  Have a door on either side of the front of the trailer big enough to slide the chuck box to slide into.  Have a fairly good sized rear cargo door that could double as a step, and two side bunks that fold over the top for travel mode.  When open, the bunks would either flip up and over or detach and be stacked on top.  For support either have fixed poles similar to a popup's bunk supports that connect to the sides of the trailer, or adjustable ones that touch the ground.  The army tent would attach to tie down points around the bunks and platform, and the guy lines would be staked to the ground for stabity.  Maybe the cargo door could also fold down to a step.  I would imagine you could easily sleep at least four in there.  A cover would go over everything to keep it dry for storage and travel (similar to Livin' Lite trailers).  If done right, I'm thinking it could pull double duty as a regular cargo trailer if the bunks and platform were made to be removable.

Other possibilities are making the tent sides extend down to the ground to disguise the trailer as a taller tent such that the tongue would be the only thing that would be exposed.