With both decks on, I could be an obsessive woodworker again.
First I shimmed up any really large gaps with thin pieces of wood, epoxying them on. Then I routed all the edges.
Once I sanded down the bumps and the previous coat of fiberglass, there were still some larger structural gaps that I wanted to fill with thickened epoxy.
Some of my epoxy kicked off Before Its Time with billows of smoke. Exciting.
I filled the small spaces and the screw holes with latex wood filler. Filling small cracks is more than aesthetic, when the fiberglass goes over the decks, any cracks or spaces will create air pockets behind the fiberglass. That’s bad.
Then I sanded everything smooth as butter with an orbital sander. Fancy.