2016 FOREST RIVER PALOMINO Tires Problems

I WAS PULLING MY TRAVEL TRAILER, A 2016 FOREST RIVER VIBE 315BHK, FROM GARNER STATE PARK IN CONCAN, TX TO CONROE, TX. HEADING EASTBOUND ON HIGHWAY 90, I EXPERIENCED A BLOWOUT IN THE DRIVER SIDE REAR TRAILER TIRE WHICH IS LABELED AS A CASTLE ROCK ST225/75R15 LOAD RATING D TIRE. I PUT ON THE SPARE WHICH IS THE EXACT SAME CASTLE ROCK TIRE AS THE TIRE THAT HAD JUST BLOWN OUT. IT HAD NEVER BEEN USED BEFORE AND HAS ALWAYS BEEN COVERED. THIS SPARE TIRE BLEW OUT ON I-10 IN TX JUST PAST LULING, TX AT MILE MARKER 649. AT THIS POINT, I HAD NO SPARE SO HAD TO CALL A ROADSIDE ASSISTANCE COMPANY AND PURCHASED 2 NEW TIRES, THUNDERER ST225/75R15 LOAD RATING E, TO REPLACE THE ACTIVE AND SPARE TIRES. THE FAILED TIRES HAVE NEVER EXCEEDED THE SPEED OF 65MPH, THOUGH THEY ARE RATED FOR 75MPH. I ALSO CHECK...