The Carlisle HD is the new gen ST tire from them. With 10/32" of tread depth vs Endurance 8/32" of tread depth this will give you more miles of service. Many rvers don't go by mileage anyways but just age so tread depth doesn't mean much to those like one poster says his trailers tires were 6 years old with 5k miles on them
I see the HDs are more popular for this reason on a couple cargo/enclosed trailer forums where some say their getting 35k-38k miles of trouble free service from the HDs. This type trailers are usually work around big city construction types....not doing long hauls across country.
How can we tell if the ST tire brand is bad ?
Two ways I've used.
One is check out NHTSA tire complaints website for the brand your having issues with.
And when your have blowouts/run flats/tread delams on a brand xyz tire on work trailers/rv trailer.....then use the same tire maintenance program with a different brand/type tire and don't have any more issues.