Duals can offer some safety or reliability redundancy in the rear that singles in the rear can't ... even if loaded heavily.
I once drove our Class C very slowly for about five miles with a flat outside rear dual. Talk about a squishy feeling on the good grossly over-loaded Michelin inside dual tire ... but that same tire went on for tens of thousands of additional miles with no problems. Way to go Michelin!
However our Class C is a small one (24 foot), so each Load Range E rear tire is a ways from being fully loaded. I was able to get to a repair facility so I didn't have to use road service or try and change the tire myself. I was also driving those five miles with that blown out rear tire on a highway - not offroad over rocks.
Also, a few years ago I drove our Class C on an extremely rocky 4X4 road in Death Valley. I drove very slowly so as to be able to pick our tire paths carefully, so it can be done ... at least if you're careful enough or lucky enough not to wedge a rock in between the duals.
