Diesel DRW. Backroads of Utah with those very heavy and large campers, IMHO, wouldnt even think of gas engine. Diesel has so much more pulling power. You have heard stories about rocks getting caught between dullies and blowing both tires, have you heard what happens when you lose a single tire? Dually gives you redundancy and a bit more safety margin. I would probably skip the super single. You must remember it takes a fairly large rock to get stuck between dailies, you will know when you drive through rocks of that nature especially with those large campers. Actually, you will not be doing much, if any off roading with those campers, they are just to large and heavy.
Driving a dually is not much different than driving a SRW, just have to be mindful of the little extra width. And that extra width also helps stabilize the load.
550 would be the way to go with those campers.