2004 COACHMEN CHAPARRAL Tires Problems

I HAD TWO CARLISLE TIRES BLOW OUT IN THE LAST 6 MONTHS. THE TIRES WERE INSTALLED ALONG WITH 2 OTHERS ON MY 2004 COACHMEN CHAPAREL BY A TIRE DEALER IN NOVEMBER, 1907. THE TRAILER MANUFACTURER SPECIFIED ST 225/75R15, LOAD RATING D TIRES, BUT THE TIRES I PURCHASED ARE ST 225/75R15 LOAD RATING E. THE FIRST TIRE BLEW LAST FALL ON A TWO-LANE STATE HIGHWAY CAUSING SIGNIFICANT DAMAGE TO THE TRAILER. THERE WAS NOTHING LEFT OF THE TIRE BUT THE SIDEWALLS. THE SECOND TIRE BLEW THIS JANUARY, 2011 ON INTERSTATE HIGHWAY 10, CAUSING SOME DAMAGE TO THE TRIM AT THE TIRE WELL. THE TIRE WAS INTACT WITH A LARGE HOLE IN THE SIDEWALL. THE REPAIRMAN SAID THE TIRE WAS FAULTY AND THE BLOW OUT WAS NOT CAUSED BY A ROAD HAZARD. IN BOTH OF THESE CASES THE TIRE PRESSURE WAS CHECKED BEFORE THE TRIP AND HAD 80 PSI WHICH IS RECOMMENDED...