Blowing tires on 5th wheel

Ok, from the guy who always read about tire problems and believed people checked pressure after driving, thus were not at max cold pressure and experienced tire failures due to under inflated and overloaded tires. Today, I was the most lucky person on the road. I really did not need it, but I pulled in for fuel and a driving break and heard the hissing. 2009 Jayco with orginal Goodyear Marathons. I check tires daily, and when I left Green Bay WI this am they were fine. The tire must have broken an internal belt as the center was "hunched up" and it had a deep wear area the size of my hand just off to the outer 1/3 of the tread only about 6-7 inches long along the tread. The rest of the tread in that zone is uniform. The leak was near the edge of the tread and I could see no foreign object or indication one was there and had been ejected. It appears that it was leaking air from the start of the complete tire failure. Had I not heard the hissing, that tire would have failed before I reached home, no doubt causing RV damage. Now looking for replacement tires...oh boy.