Blowing tires

Our trailer has blown 3 tires in the past year. All on the same wheel, the right side front axle tire (it has two axles). The first time this tire blew, the whole tread came off, and chewed up the wheel well of the trailer :(. We figured it was old tires because they were the original tires that came with the trailer, and were 5 years old. We bought ALL new tires for the trailer in March of this year, Goodyear Marathon, same as what was on the trailer. With just 1500 miles on the new tire, the same wheel blew again, right side front, but didn't chew up the wheel well. Another new tire, and 500 miles later, this 3rd tire, blew again, tread coming off, and chewing up the wheel well in the process :M. During this whole ordeal, tire pressures were always checked pre-trip, and psi was inflated at manufactures 50 psi. Tow speed was kept at 65 or lower. We keep very little in the trailer, and haul equipment, luggage, etc in the truck. Does anyone have any idea why this is happening always with the same wheel :h? I hope I've given enough detail here. If not, let me know.