Is that Sunseeker fiberglass roof one piece, and nicely crowned ... versus just flat and made up of more than one piece?
You want a one piece and generously crowned fiberglass roof for additional long-term strength and leak protection.
Just as an observation: Winnebago products have been noted down through the years for their one-piece fiberglass Class C roofs. However looking carefully at photos on their website, it appears as if even they are selling some Class C motorhomes now with roofs with little or no crown in them.