Hi Jim,
We have owned a number of motorhomes and currently have a 5th wheel. The tires that you see on larger RVs are designed to go a lot of miles... seems that they often "time out" before they wear out. The covers are popular, and probably do help. I say "probably," because we did use them on a couple motorhomes, but generally traded before we wore out the tires.
We are currently in an RV park in south Texas, and I don't see anyone with tire covers here (but most of the RVs have moved north). We were in the Phoenix area with our 5th wheel the past two and a half months, and we saw lots of RVs with the tire covers.
Trailer tires like we have on our boats seem to last us less than 20,000 miles; we are on our third set in just over 7 years. We do wear 'em out before they get beyond their useful life. We had a blowout on the boat trailer a year and a half ago. The road service guy who came out (first time I've had to use my Boat US towing insurance) told me that he has never had to change out a worn out trailer tire... they always come apart from age... and it is happening more frequently, probably due to manufacturing changes. He suggested that trailer tires be changed every 3 to 4 years, even if the tread still looks good. (And, no, he didn't sell tires.)
My take from that is that covers might extend the life of tires that sit a lot. UV exposure makes a difference. The other option is: haul that trailerable boat around and try to wear out the tires before they time out.
😉
If you decide to go with tire covers, go with white (we have seen white and black, as well as sun screen material attached over the wheel wells of RV. Here is a tread on that from FMCA (Family Motor Coach Association)...
http://community.fmca.com/topic/1912-re ... ure-study/
and from another RV forum...
http://www.rvforum.net/SMF_forum/index. ... ic=50257.0
Best wishes,
Jim B.