Tom, (West Chester, PA)
Tom, I have had good success over the years using a product called 303 Aerospace Protectant. It used to be called AP 303 in the old days. It's available at any well-stocked RV retail store. Avoid products containing silicone or any other type of petroleum distillate which can actually dry out the tires making the thinner sidewalls more vulnerable. Ever notice a real "shiny" finish on a recently dressed tire? Yes, it looks nice, but chances are it is not helping to extend the life of that tire or protecting it from ultraviolet sun damage or that nasty ozone that is common in many locales. 303 will not leave the tires shiny, but it is effective. And still consider some tire covers for the next storage period also. You can't beat double protection.For more detail on tire protection, see my response to Murray.