Folks usually have good luck with the Marathon's. If Goodyear is still doing it, they did have one of the best warranty programs going. There are a few reports on this Forum of owners having blow outs with damage to the RV. Goodyear was stepping up and paying for the replacement tire and the repair cost.
If you do have a heavier TT, you may want to do some math and see what the numbers tell you about weight on the tires, Typically, a Mfg puts rubber on that barely meets the weight handling. That, IMO, is a disservice to the consumer. A load range D or E tire is not all that more expensive than a C rated tire. FWIW, I replaced mine a couple of years ago with Carlisle RH Trail Load range D tires. I have more than enough headroom with weights and these newer Carlisle's get pretty good reviews.
I'm married to these rims for awhile or I would have probably upgraded to an LT tire, just for the peace of mind. As it is, the Carlisles have a higher speed rating than typical ST tires. That may or may not mean better durability. Still to be determined after another 3-4 years of use.