This Dynamax F-Series ordered in a limited-slip rear 4X4 with the 10,000 lb. towing option sure looks like something you might be interested in -> note that it comes in several lengths and floorplans:
http://dynamaxcorp.com/products/IsataFSeries/P.S. I can identify first hand about getting stuck in a standard Class C. The past January I was riding with a friend close to Quartzsite in his 24 foot 2WD standard-differential E350 Class C when we got stuck in an extremely rocky wash. He got us stuck due to driving it wrong in the soft stuff. (You gotta keep those front wheels in line so you don't plow them, and 2nd gear is best to balance torque from a standard differential so as to keep even distribution of power to each set of duals!)