I don't think it's
fiberglass, could be wrong, but another example of someone thinking outside the box!
The classic Aqua-Trail “Terra Marina” was only in production for one year, from 1959-1960, and only 35 were ever made. This camping trailer doubled as a house boat, and was completely self-contained, to make towing it or rowing it a breeze.
That's all I know
Spanke