Tire brand issue
A ST tire is still a ST tire regardless of brand or country of origin. I would look for LT tires for that size trailer.
What size tire is needed ?? Dunno but....... A 13000 lb 5th wheel trailer can have 2600 lbs of pin weight which may leave 11400 lbs on the trailers axles or 2600 lbs per tire.
Your in Goodyear Michelin XPS or Bridgestone R-250 at 3042 lbs load capacity.
If that trailer is on the road and long trips don't cheap out on tires
Edited for wrong tire brands and numbers...thanks goducks
....Jim