Re: Help for DIY fiberglass hatch cover
If Fasters idea won't work, get some foam core and make a duplicate of the existing hatch. You can stick the pieces of foam together with hot melt glue. Once you have it shaped the way you want, start laying on glass. Ordinary polyester resin is fine for this application.
Personally, I'd find a commercial aluminium & plexi hatch that would fit the curbs with a little tailoring, but that's just me.
I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.