Thanks for the tip Tom.
I was planning to coat the underside of the decks in the areas that aren't going to be epoxied to underlying lumber. I wanted to pre-coat so I didn't have to try to epoxy coat the underside of the decks by hanging upside down through the hatch

But I still want to be bonding to bare wood in the places where the decks bond to the frames/stringers. this was pretty easy with the seat tops since there are only a couple of spots where framing crosses the panel (since the seat tops are bonded all around the edge it was an easy matter to mask off the outer edge when pre-coating). Using the screw idea I can pre-mount the deck pieces and scribe the frame outline on the underside of the deck then remove the screws and pre-finish the underside to the scribed lines.
Come to think of it there's no real reason to wait for the "pre-finished" areas to cure - I can scribe the glue boundaries, then coat the whole underside of the deck piece with thin epoxy, then go back over the areas that need to be bonded with thickened epoxy and screw the deck back down.
Hey man, you just saved me a day of epoxy work!

Sorry for the lengthy post but I was figuring out the process as I was typing. Maybe it'll help a fellow stitch-and-glue newbie out there somewhere...