Goodyear Marathon tires

Our Jayco 5th wheel came with Marathon tires and the only reason we replaced them is that they got to be 7 years old. Our next set of Marathons were replaced after 6 years with no problems at all until very late in the life of one of them; it started showing signs of uneven wear. Our current set was a rushed purchase and we couldn't find locally four Marathons that were not made in China, however after several trips over about 10,000 miles all together they are wearing evenly, in fact hardly at all (measured in several places across the tread with a depth gauge). Three factors may contribute to our success, though, are that our trailer is very light, we keep the tires covered during storage, and we are religious about checking wheel lug torque and tire pressures every time the rv is moved. Our neighbour has a very heavy toy box and he has had blowouts on almost every outing from the day he picked it up new from the dealer (not with Marathon tires, but I won't mention the brand name, to avoid prejudicing anyone's conclusions). I don't think any ST tires, regardless of brand, can handle a great deal of weight.