Great topic, albeit kind of old...
I am very interested in the 4x4 sprinters... Unfortunately it isn't in the budget right now, time or money. Someday..someday... I envision traveling around the USA seeing many of the seldom seen corners of the national parks, camping on remote beaches; Portsmouth Island, taking/camping on the many remote "roads" and passes in Colorado and Utah.
After reading some of the comments and based on my novice experience of off roading in a 4runner and many years riding dirt bikes. I have no doubt you can scare the pants off yourself before the vehicle gives up, no mater if your in a subaru or a unimog! I have been in some situations that make me uncomfortable in my stock Pro 4Runner. I can only imagine what these guys with stock Rubicons on 37" could get into!!!
Anyhow, some commenters mentioned towing a off roading rig. That would definitely allow for a more comfortable and roomier RV... My main concern is comfort while in transit and ease of driving.. My main concern with a standard class C RV is even on a slightly imperfect unpaved road it wouldn't be very fun. Not to mention lack of beach driving...