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.