I think StableLoads will make the most difference if you want the truck to be level or you run air bags.
Although possible, I find it unlikely that you will carry an empty camper into the back country. Because of that fact, I think you should go for the 19.5s now. Of course, you can ask some of the guys here or search to find out what their TCs weigh, but I'm pretty sure you are going to be weight more than you think.
People can tell you how unpleasant it is to have a blowout and in the backroads with large rocks, there is more of a chance to blowout a sidewall as well. The 19.5s are tougher tires and wheels.