I have a 2000 28A Four Winds Class C motorhome with 26000 miles on it. I have replaced the front two tires, but the back four tires look to be in excellent shape both tread and sidewalls. I have always kept the tires covered when stored. I have read several places that you should always replace tires after seven years no matter the condition. I hesitate to spend the money when they look so good, but I don't want to have to worry about them on a trip. Also, what is the rule on rotation and how? Any comments on this subject would be appreciated.