2002 ALFA SUN Tires Problems

WHILE DRIVING MY TOW VEHICLE (PICKUP) PULLING A 5TH WHEEL TRAILER, THE TIRE IN QUESTION BEGAN TO SMOKE AS SEEN FROM MY SIDE MIRROR. I IMMEDIATELY PULLED TO THE RIGHT SHOULDER OF A STATE HIGHWAY AND STOPPED. ON INVESTIGATION, I FOUND THE DRIVER'S SIDE FRONT TANDEM TIRE WAS FLAT AND HAD 1/3 OF THE TREAD SEPARATED SLAPPING THE WHEELWELL OF THE TRAILER (BLACK MARKS) . AAA WAS CALLED TO REPLACE IT. THE TIRES WERE ALL CHECKED AND INFLATED TO 80 PSI PRIOR TO LEAVING ON THE 130 MILE TRIP. THE TRAILER HAD BEEN WEIGHED IN TRAVEL CONDITION AND FOUND TO BE UNDER MAXIMUM GROSS VEHICLE WEIGHT. THERE WAS NO INDICATION OF AIR PRESSURE LEAKAGE OR UNUSUAL TREAD WEAR ON THE TIRE WHICH HAD BEEN ON THE VEHICLE FOR 4 YEARS WITH APPROXIMATELY 10,000 MILES ON IT. THE TIRES HAD BEEN STORED IN A COVERED CONDITION THROUGHOUT THE LIFE ON THE...