Quick simple question. Our tire covers worth the expense that they cost? Do they actually prolong the life of the tires?
Maybe a simple question, but not a simple answer.
Lab tests show that long term exposure to ultraviolet will shorten the maximum life of a tire. That's a proven fact, but it takes years, not days or months. A bunch of other things will also shorten tire life, and that's where the practical answer gets less clear. If the tire dies of some combination of other factors before the ultraviolet causes enough damage to be fatal, is it worthwhile to reduce UV exposure? And how much UV exposure can you really prevent? Obviously UV gets to them while you drive, and also during shorter term stops if you don't apply the covers.
Rv tires that get driven on reasonably often and don't wear out due to mileage will probably last 5-10 years, and some few even 12-14 years. With or without being covered. Tires that sit in one place and rarely ever get driven on typically don't last long anyway, though they may continue to hold air until there is an attempt to drive on them again. Covering a tire that sits in one place for extended periods and is constantly exposed to direct sun can probably be of benefit. Whether it's enough to justify the cost is harder to say, and no data exists to prove or disprove that. Covers for 15-16" tires aren't expensive, so not much financial risk there.
The most obvious effect of UV exposure is fine surface cracks (called weather checking). Weather checking on the surface rubber is considered a cosmetic problem unless the cracks get deep, say 1/16" or more. The Michelin RV Tire Guide has some info on this and other factors:https://www.michelinb2b.com/wps/b2bcontent/PDF/RV_Tires_Brochure.pdf
So, it's clear that you can take UV-preventative action by covering the tires as often as practical. It really can't hurt, and in some circumstances it may help. As a practical matter, heat & air circulation are probably not a concern with any of the products available, or even any home-made design. White or silver is better than black, and loose is better than tight, but you probably cannot enclose a tire enough to have much negative effect anyway.
At this point I need to say that I am not a fan of covering tires, even though much of my life has been spent in the Sunbelt. I've never been one to let them sit for months or years, so that is probably a factor. I replace tires at 7-8 years of age regardless of miles or other factors, simply because age itself is a factor. I don't know if covering them religiously would lengthen that time span or not.