When we were in the market for tires for our HTT a couple of years ago - before Rocky - our local, reputable tire dealer suggested Westlake. We'd never heard of them, but he said he'd sold many sets with no problems reported. But.....at the time, there was a thread running re tires and several reported problems with Westlake, so we went with what we'd had excellent service with....Greenball Transmasters. They were OEM on our HTT, we replaced at about 4 years with the same and then at 3+ years due to a long trip scheduled. FWIW, DH is diligent about checking torque and tire pressure before we leave the driveway and repeats if a longer trip. Also, it's very rare for our speed to exceed 60 - 62MPH. Have no idea what the OEM is on Rocky, but when the time comes for new ones, Transmasters will get another good look. Will also consider LT vs ST.
To the OP....do you know the true age of these tires?? Because the trailer is a certain age, does not mean the tires are the same. They could have been sitting in a warehouse for a couple of years or more, making them ready for replacement a year or so after they were put on. Suggestions for replacement age varies by post, but most say 4 - 5 years. We're on the 4 year side as extra precaution. Sorry for your friends experience.