I have a 25' gooseneck horse trailer, most recent of many, and I have usually kept my tires 3-4 years before replacing. Now on my second set of Goodyear Endurance E rated and I'm very impressed. What is "your" recommendations for how long I should keep these on my trailer that gets about 8-9000 miles of towing yearly?? My first set looked almost new after three years, and I'm through 2 years on the second set and they also look new. What are "your" guidelines as to when to renew?? Thanks.