I have never covered my tires. Depending on circumstances, I either use my coach most of the year (like snowbird runs to Fl or AZ) or it sits all winter. \
I have always run Goodyear tires (came with the coach...I have no reason to move to another brand) and they claim an additive in the RV tire that blocks UV rays, etc., etc..
I do get new tires tho, every 7 years or around 25 thousand miles or so (sometimes longer) when the ride itself becomes uncomfortable. (tires become hard)Plenty of thread left, tho....