Here is a design along the same lines we're working on right now. The idea is a rolling camp box, it has a kitchen/galley area with organized storage and counter space on front and a general storage area in the rear. The tent unit mounts on top and can be used without unloading the trailer.
Here is the mockup with a couple of different tents on it
Here are a couple of build pictures. Will start filling exterior screw holes today and will start on sealing the inside tomorrow.
Chris, if you're down Corvallis way, stop by. We normally have a couple of Tent Topped Camping Trailers around to check out.