Tires for my fifth wheel.

Well we have Bridgestone Duravis R250 LTs under our Mountaineer. Time will tell, but so far I like.

Did you keep the old tires? I've always heard the Goodyear is very good about covering the tires and any damage done. Be worth checking with a dealer. I also agree with amxpress; you may have been under inflated. Highway driving, heat generation, low pressure. Not a good combination. Sorry for your troubles, and good luck.

It appears that all Montana Mountaineer's used 235/80R16E tires and they need to be set at 80 PSI cold. I don't know if 5 lbs too low will cause all the problems you had since other variables come in to play as well such as your traveling speed, how heavy you were and what the ambient temperature was. But the biggest contributor was simply you were running ST tires. They are just flat unreliable when used on the heavier 5th wheels. We changed from the OEM Chinese made 16" ST Tires on out Montana 3400RL to 16" Bridgestone R250 Duravis LT tires and have not had trouble since. They will run around $200 each. I believe the Maxxis ST Tiresare quite a bit more expensive. I will never install another ST tire on a 5th wheel or trailer.

1) What size tire do you have on your Montana?
2) I would be willing to bet that you are running way under inflated at 75 psi.
You will receive numerous suggestions on installing LT trailer tires vs ST trailer tires. Your marathons are ST trailer tires.
I run Maxxis M8008 ST 16" tires on my fiver. I really like them and I could afford them. Maxxis is the ONLY ST tire to run. Two popular LT trailer tires are Michelin XPS Ribs and Goodyear G614 trailer tires.
Stay away from any ST tire made in China as they don't have a great track record. As mentioned, Maxxis is the ONLY ST trailer tire to consider if you choose to go with ST tires.
Run the ST tires at Maximum pressure. Be sure to have them balanced, too.