I've seen different types of plastic roofs used for RV's.
Some of the plastic roofs are made from a polycarbonate while others are made from fiberglass, with strands of fiberglass combined with fiberglass resin. A polycarbonate is a thermoplastic which is approx. four times stronger than fiberglass.
From searching online I see paints designed to work on both or more specifically on one or the other.
I think perhaps it's a polycarbonate roof, however I can't determine for certain because of the headliner. Usually fiberglass roofs you can see the fiberglass strands at least on one side while the other side may be coated or painted with something to make it smooth.
I've worked on boats but mostly wood or metal, not much with plastic.
I can remember a boat from years ago that was made from concrete.
It was made from some sort of specialized concrete and wire.