Bluebird, I had American made Marathons on my 24-5N, I had Chinese made on the 29-5E, over more then a decade (combined) I had zero problems.
But Northwoods doesn't overload their rigs, your's has a dry weight of around 6000 lbs and a max loaded weight of around 10000 lbs. I don't think I ever got mine past about 8000 lbs.
I also kept my speed between 60 and 65.
Discount tire (local) carries a Carlise ST tire that is speed rated for 75 and has the same load rating (E) as the old Marathons.
They also carry some cheaper ST tires, but will try to talk people out of using them.