Check out the Jeep campers available here:
http://www.livinlite.com/jeep-camper-overview.php
The website info will show you what's taken into consideration for true off-raod trailer capability. IMHO, it seems to mainly focus on trailer ground clearance and a full-swivel coupler (ie no ball mount to pop off while running down that dry creek bed). Shovover made a good point, too, about checking out the Australian camper options. The Aussies seem to have a lot more wild open boondock type camping than we do here in North America, and their toys reflect that!
FWIW, you might be able to mod a standard tent trailer to suit - lift kit, off-road tires, off-raod coupler, maybe beef up the axle? Depends how hard you intend to be on whatever you're towing, I think. The end result might be a bit heavier than you'd like, though. What are you towing with?