I've done some vids on this and some decks with KiwiGrip. Yes you can put it directly onto the fiberglass. But you still need to prep it. You can see how on my channel.
jorge ramirez ...It is not hard to clean as long as we use the long soft bristle brush. We also painted over it with the deck paint (semi-gloss or satiin) that you can find in Home Depot and after that cleaning is even easier.