ST tires are supposed to be used on travel trailers and 5th wheels. Check out
https://rvingwithmarkpolk.com/2012/1...s-vs-lt-tires/
When we bought our 2006 Montana a couple of years ago, the tires needed replacing, because the tires on the unit were 6 years old. I started searching on line, and found Load Range G, ST tires at Discount Tire (the trailer was originally supplied with Load Range E). They are a Hartland brand, rated for 81 mph. After 2 years and 20,000 miles, they are doing well.
There are several other websites that outline why you should use ST tires, not LT tires on a TT or 5er.