Tire Blowout problems of the 1996 Ford E-350

During the past 3 years we have had 5 tires fail on our 24 ft. Motorhome while traveling at 60 mph on the open road. In all 5 cases the belts appeared to seprate from the tire and cause the tread to come off. Three times the tires blew out while going 60 mph. I took the tires to firestone dealers in palm springs and lancaster, CA to be replaced, on each occasion I asked if this was a problem with these tires and was told it was not. In in April 2000 I replaced the 2 front tires with load rate e(all original tires had load d. I was told by the firestone dealer this would help the problem. ) in palm springs after I had a blow out on the front. In August I replaced the other 5 tires with load rate e after having 2 blow outs in one day, both on the rear. . (dot number: vdil 1xb 4 tiresize: lt22575r16).