Anyhow, today we got ‘er done. We cleaned and leveled every gutter. I cut every unique hatch rim out of White Oak and dropped it in each gutter, pre-rabbetted for the lid. Once we had everything working okay, coming in flush with the decks, etc. etc., I cut the miters and shimmed them all into place with tongue depressors and stirring sticks, keeping them off the edge of the hatch hole, and off the edge of the hatch lip. Just so.
Then took each one apart, 5-minute epoxied every joint, and reassembled them with all the shims holding them just so again.
Once the epoxy kicked, I carefully removed each frame, laid it upside-down on each piece of plywood designated for that hatch, marked the plywood, cut it, and epoxied it into the rim. (Yesterday we fiberglassed and flow-coated these lids so the interiors of the hatch lids are now done.)