All the answers you've received so far are good and accurate. Unless specifically built by a specialty company for "Out back" exploring and camping, on any coach, Class A, B, or C, you'll eventually start seeing loose cabinets, loose dash parts, many, many more squeaks and rattles and more. These type of structures are barely built good enough to handle Americas "really nice" (just a bit of sarcasm there) roads. Will any of them work, sure. It's just a matter of time, depending on your distance of travel off road, the speed at which you do it, tire pressure, type of suspension (air or spring) and frequency of travel in the outback.
A diesel may be able to actually take the wash board better due to the type of suspension most have but, they have their own issues to deal with. Many, especially the rear radiator types, will dust themselves to death in an off road situation, due to the fan back there and, the amount of throttle the driver is using, even at a slow pace.
We've done it for years but, again, it's not without potential issues. Even with our present coach, an '04 Itasca Horizon 36GD with the C-7 330HP CAT, I'm really hesitant to go off roading with it due to limited ground clearance and just the fact that, that kind of terrain is hard on cabinets, mounting systems for a zillion items and a whole lot more. It's just a matter of if one accepts the POTENTIAL issues that may, or may not crop up. Good luck.
Scott