Tires: something to keep tires from dry rotting, physical appearance, best bet

Question
I have a trailer which is not used very often. I am concerned that the tires will dry rot.  Is there anything I cn do to keep them from dry rotting? Do they sell anything that cn be sprayed on the tires?
Also, I've heard that some of the tire sprays for shine are not good for tires - is that true?
Thank you.

Answer
Carolyn,

Given what we've learned from the Firestone experience, your best bet is to track the tire's age and not the physical appearance.  If you live in a cold weather state (Michigan / Minnesota) then 10 years is the limit, and if you live in a hot weather state (Arizona / Florida) it's 6 years.