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 ...
Feeling warm and being too hot are completely different things, especially if going by feel. Unless you have a lot of stuff shoved in the camper or extra boxes outside, I would seriously doubt you are overloaded with a Lance 850 and 18" tires. I have looked at that camper for my truck running the same basic tire and feel I would be about 400 pounds below tire load capacity.