At the risk of hearing flames from the extremes, how long should I really expect TT tires to last? My situation: I have a 2005 Jayco Eagle 298BHS (8000-9000lb loaded) with Maxxis M8008 ST225/75R15...
According to the National Highway Traffic Safety Administration, recommended service intervals are 6 to 10 years based upon the manufacturers recommendation. Visible inspections will not tell you how the internal structures of the tire are wearing.
My own personal opinion which should be taken with a grain of salt is that I'd replace them after 5 years in very hot climates, and 6-7 years in cooler climates.