Time for tires?

Lack of regular use is a big killer of tires. I learned the easy way. After 5 years since I bought the truck, I decided to use the spare and buy another identical tire for the other side of the truck. The tire had been under the bed of the truck. It looked good. Still had pressure. I put the tire on the truck as planned. Over the next couple of weeks it took a couple of short drives and prepared for a long trip. Then I noticed the previously good looking tire was cracked all over. The local tire dealer told me that tires need to be used regularly. The use and heat has something to do with internal chemicals that come to the surface and protect the tire. Sounds strange. But then again a tire in use for 5 years might have had wear but should not have had cracks appear everywhere.

I have been told 303 protectant will help but you need to spray all surfaces of the tires before putting the RV away for the season.