I've been using plugs to repair tires on cars, trucks, heavy equipment and equipment trailers for almost forty years -- steel belt, bias, whatever. I have never given a second thought to the integrity of a repair in the tread, and I've never had a problem. I have plugged a few side walls, also, but those tires were fairly quickly replaced.
I have never plugged a tire on a travel trailer, though, but I would. I think I would keep an eye on this plug and replace the tire fairly soon. I'm older than I used to be and am now a little more cautious.
Bruce