On my 30'+ Class C RVs I always put 225/75r16 COMMERCIAL (121) load rated tires. These each carry roughly 500lbs more than e-Load (115) rated tires. That's 2000lbs more weight buffer on the rear axle. I'm always surprised (disappointed) at how little weight buffer E-load rated tires have on the rear axle of a 30-31' Class C RV straight out of the manufacturers.
Note: You should never overload your axles. But all else being equal, I would rather have tires (Commercial 121 rated) that can carry 2000lbs extra. You never know when you might have a situation where they are slightly underinflated. Or you might have one get a leak and it takes some time to notice/etc (TPMS helps with this).
The last set I bought was from Big-O tires. I believe I paid ~$180/tire.
Good luck!
Chris