First question I have, same tire on same axle? Random tire placement on trailer? Quote, we are not overloaded", did you scale your rig to prove this? Is your trailer level when connected and towing?
Last and most important, how fast do you normally tow? Be honest, answer these questions, and maybe we can help.
Also checking tire pressure is never enough. Did you ever get down and look at the tread? A bent axle will cause wear on the inside or outside, of a tire, and I have seen several come from the factory, where the axles were made upside down, causing severe tread wear on the inside of the tire. Cords showing, blowouts in 1500 miles, or less, not counting 500 miles from factory to dealer.
Just some things to check. Let us know.
(I am a part time tech)
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT