Sorry I got your project confused
Smitty, I misunderstood, I thought you were working on hatches rather than ports. Let me answer your followups in reverse order:headliner material--the frp stuff with the stubbly texture that I got from Home Depot is rather flexible, but it's also very tough and should not sag once it's screwed in place. I think the flexibility will actually help keep it from pulling the screws loose the way the plywood backing did. The frp pieces I used to replace the little leather-covered cardboard pieces above galley and nav station are hard enough in place that I could punch them and not have them push in.leaks--I have trouble believing the fixed ports would leak--there must be 2 inches of adhesive between the edges and the interior. Myself and another owner have compared notes and found a lot of surprising little sources of leaks that are more likely: --dorade box; some our our boats had the dorade box "floor" (cabin ceiling piece with vent shaft) caulked in place rather than glassed, and leaks from that will run down the coach roof liner to the area where you see water. Try pouring some water in the dorade box and see if you get a leak. --ceiling; I have a place in my ceiling where a saw cut through the fiberglass to the balsa core when they trimmed the liner; the crack in the deck above it causes water to drain through the cut and drip down my headliner. A shot of epoxy will seal it.and that brings us to source 3, your starboard Beckson port. A leak at that port will dribble down between the liners to about the area you're talking about. It sounds like you have to replace the ports anyway, so why not complete that first and see if it does the job? (If you use Beckson again ditch the originals and use the "rain drain" model, which the factory should have used to begin with!)I got my Beckson ports off last week and found that the factory had stuffed epoxy in the liner around it to seal it from leaks, but that doesn't mean there can't be a crack. There was an article in a magazine recently about how to replace fixed ports--not a pretty job, one you might have a port specialist do if you have one available (it's not caulk holding it on, it's a tenacious adhesive that would probably require destroying the old port to get off).If your forward hatch is the only one leaking, then you're not bad off, because there's no cored deck in that area and nothing is getting damaged. I'm not sure what you meant about sizes above, but I'm pretty sure the current Lewmar size 20 and 40 Ocean series hatches are drop-in replacements (okay, but maybe with different screw hole positions to be drilled).