Airstream installs Michelin LT truck tires on their brand new trailers, so there must be a loophole to allow an LT designated tire to be used on trailers pulled on the road, as well as sold new.
Airstream has been the Cadillac of travel trailers for decades, so they have more experience than anyone that is currently spouting opinions on the net.
The video I watched showed the guy having his Airstream trailer getting 4 new LT Michelin tires installed at Discount Tire. If you've ever bought tires at Discount, they are sticklers about age of tires, whether a tire has an injury in a critical area that cant be repaired, ETC. I don't see Discount installing LT tires if it opened them to liability, or if DOT was going to make an issue of legality.