Eternabond may be junk, but in the RV world, it is about using what sucks the least for a solution. They even have 48 inch wide rolls, so one can do the whole roof with three of them overlapping.
My solution? I spend some money for materials and labor to pay a RV expert to reseal the roof twice a year. Leaks are my worst nightmare, because they would utterly destroy my TT.
If I wanted the best solution, I'd probably drive to Florida, hit rvroof.com and have them do their magic with a one piece, seamless coating. Similar if there is a Rhino Lining RV place nearby. The "real" solution would be having a rig that has a metal or fiberglass roof. Rubber roofs are basically expiration dates stamped on the rig, almost guaranteeing they will leak and rot to scrap value within a few years.