.might want to check in the Trailer subforum, lots of really interesting stuff in there.
http://www.expeditionportal.com/forum/forums/42-Expedition-Trailers
Their 'Baja' series seems to have the ground clearance you'd want.
But for offroading you'd probably want the shorter version sans ATV deck.
They seem like a slightly smaller version of Fleetwood's 'Evolution' trailers. My neighbor has an Evolution II that I'm itching to haul to Death Valley and points north