Your trailer came OEM with 6k axles. The trailer weighs 12000 lbs minus 2400 ? lbs of hitch weight the truck carries = approx 2500 lbs per tire rolling down the road so any of the LT235/85-16 E or LT245/75-16 E that has been recommended on this web both have 3042 lbs of capacity and will give you over 20 percent of reserve capacity.
The Bridgestone Duravis R250 or the Duravis M895 are both a all steel carcass commercial grade tire and make a excellent choice for a tire on a trailer.
My trailer came with 5200 lbs axles and 2480-2500 lbs per tire requirement. I went with a BFG Commercial T/A LT E and ran the first set 55k miles in seven years with no issues. I'm close to 40k on the second set with zero issues.
Upgrade to a 16" LT E and forget about ST tire issues.