cleaning fiberglass roof top?

Indeed, it is ugly. The finish may very well indeed be Gel Coat -- I don't know what Roadtrek uses to finish the fiberglass roof. Would I need to sand it all down to a smooth finish and then re-Gel Coat it again? It's not smooth at all the way it is now -- very rough and "patchy." Try Bartender's Friend to see if I can get it smooth enough to have it Gel Coated again? I'd like to do part of the work myself, if that's possible.

Thanks.