Thanks guys,
Lenm,
The boards are sepele, they're part of the sub structure of the deck, a slight deviation from the plans and will be covered over. . For whatever reason, my planking had pulled the shear clamp out about .125" between the frames in the cockpit so I glued some 2 x 3 stock against the clamp to straighten it. I didn't want the 2 x 3's to remain in the finished boat so I needed to transfer that load to the covering board and wasn't confident that the .375" ply would be up for the job.
Any epoxy fairing filler can go directly onto properly prepared/ground glass work. The grinding part is why I like to trowel on filler while the glass is still green stage. I use a combination of prepared fillers and shop made fillers. With a cost around one third, a majority of work uses shop made. This project uses all alexseal products.
All the white surfaces and brownish spots you see in the preprimed photos above are fillers. The darker areas of the white fields is the glass showing through the filler, so it's a skim coat in many areas. But my goal is to achieve a fair surface without sanding any long fibers of the glass.