With input for others including those on this forum, thank you, I have reached a decision on wheels and tires. I am sticking with duels and 19.5's.
The duels are just too stable and standard for this type of truck to switch; same with the 19.5 size. I really worried about the loss of stability AND flotation/footprint on the rear axle; by going to super singles. Even with a large wide tire I still ended up with less rubber on the ground, with two tires, than even the narrow duels with four.
I will be purchasing 19.5x7.5 wheels, hopefully in aluminum to save weight. Than I will install 285/70r19.5 tires, probably the Toyo M608. This will give about 22" of tire width on the front, up from 17" and 44" on the rear up from 34". About 26% more surface area. I currently have no spare and no good place to carry one. By going with duels spec-ed out to also work as singles I now have two spares with me; stored on the axles.
I do worry a bit about the larger stiffer tire giving a rougher ride. I hope to compensate for that by being able to run a lower pressure. I have been running, loaded, 65 lb in the front and 55 lb in the rear. No issue with heat and a noticeably less harsh ride.
I will get valve stem extenders, if needed, and plan on using the Coyote automatic tire deflators for gravel roads. I am a big believer in air down for ride comfort. I have already installed the ARB duel pump compressor with quick connect fittings and hose in the under bed boxes on each side of the truck.
After this I think the next step will be to finalize a typical all up load on the camper and truck. Then off to Puhl Spring in Spokane for custom springs sized for my specific use and weight. Probably new shocks at that time as well, more research needed here. I am confident I will end up with a truck that rides well on the freeway and will handle the washboards with more than acceptable comfort.
Bottom line is that the truck and camper work very well as is. It can only get better.
