Right now, we have stock Continental 275/65R18 123 tires (max 3,415lbs) with 10K miles on them. They are mounted to stock aluminum 18"x8" 8x170mm rims (max load 3,590lbs). They are inflated to 75psi ...
They'll handle the camper great, better traction, look better and lower highway rpms by a couple hundred not that you need it. I wouldn't waste my time re calibrating the speedo. Only off a few mph at highway speeds.