45 psi is WAY underinflated for a 12 ply tire, That alone would build up heat in the tread. Also too much flex in the sidewalls. Then BOOM. Underinflation is 90% of all tire failures. If the rating calls for 80 PSI then that's what should be in them. If that is too uncomfortable for you, 10 PSI less is OK. Any less is just asking, no begging for problems.

I am with you guys - I always keep my 12ply at 5lbs below Max. and 2 spares.

When I first bought my current boat and trailer, the first thing I did was to replace the complete brake system and the tires [tri-axle]. I average about three thousand miles a year on the trailer and check bearings, seals and air pressure regularly. A few years back, I was prepping my trailer for our annual trip to Maine and noticed one of my tires had a shifted belt. I removed and replaced the tire and headed on my way. On the way north I had another tire go bad with another shifted belt. Two down four to go! While I was in Maine I went to the local tire shops looking to upgrade all 6 tires but nobody could get me a set. So I replaced the tire that went bad and figured I would deal with it when I got Home. Long story short, I had 3 more tire failures on the way home and a 7 hour trip took 16 hours. Moral to the story - I now replace all 6 tires and 2 spares every 3 seasons. Yes my boat sits on the trailer with the tires on the ground for the winter.

well ,,i am taking all the advice,,start with replacing tires,,,and keep tires inflated to 70,,,is that good for a 12 ply??
so,,,,do you think it possible that the issue is or was tires being so under inflated???
also going to check tires with level,,vertically.
yea...good idea on the water on driveway,,help tires slide
and finally,,,yes boat and trailer sit in garage when not using ,,,or pulling motors hahaha
i jack trailer up for winter time,,take load off tires etc..

your new tires will have air pressure cold and max stamped in the side wall, go off that for inflation lbs

Pavement
Concrete
Shingles over wood
Teflon sheets over wood (cheap cutting board type sheets)
Wood
Gravel

Dirt and/or grass as a last and only temporary resort

...in order of preferred parking for tires. AND keep them covered from UV rays. Look up Amfor foil tire covers on Amazon. I have at least 2 dozen of them.

I’m guessing that your trailer while statically stored allowed moisture to permeate the lower part of the tire and deteriorate the steel belts.

I always run the tire at the MAX pressure listed on the side of the tires. I always felt the stiffer the tire the better they pull, and I get the best wear.