2002 FEATHERLITE TRAILER Tiressidewall Problems

I HAVE HAD SIX BLOW OUTS OR TIRE FAILURES ON GOODYEAR "MARATHON" TRAILER TIRES IN 15,000 MILES!!! THE TIRES WERE ORIGINAL EQUIPMENT ON A 2002 22' HAULMARK ENCLOSED AEROSTAR TRAILER. THE TIRE SIZE IS: ST 225/ 75 R- 15. THE CATASTROPHIC FAILURES HAVE BEEN MOSTLY WITH THE SIDE WALLS BLOWING OUT AND ONE WITH THE TREAD BELT COMING OFF. I AM METICULOUS WITH KEEPING THE PROPER INFLATION AND HAVE VARIED IT BETWEEN 65-55 LBS. THE TRAILER IS NOT OVERLOADED (3,500 LBS.) WITH TANDEM HEAVY-DUTY AXLES. THE FAILURES HAVE BEEN ON ALL FOUR TIRE POSITIONS, THERE WAS NO UNUSUAL TIRE WEAR PATTERNS. THE TRAILER MANUFACTOR DENIES ANY PROBLEMS THERE AWARE OFF. THE LAST FAILURE OCCURED ON DEC. 17TH 2004 JUST AFTER STARTING A TRIP 10 MILES FROM MY HOME ON INTERSTATE 75. THE FAILURE PREVIOUS TO THAT OCCURED ON WEEK EARLIER WITH A TIRE HAVING ABOUT 1,000 MILES ON IT. THE...