Well, T@B trailers aren't molded fiberglass. At least, none that I've seen. Even the fiberglass version that I did see was fiberglass panel over a frame.
My wife and I looked at the T@B trailer and we decided against it for a number of reasons, not least of which was the fact that you can't stand up in them (at least, I couldn't--and I'm not that tall); and there's no bath option.
But I can see why some people would be quite pleased with the T@B. I've long since stopped questioning the tastes of other RV users. Especially since I had to tolerate the insults I had to endure from a jackass who saw my Casita
at Juniper Springs Campground in Florida. What a jerk.