My old fuel tank hatch covering the 40 gallon tank coffin was soft and very heavy from years of being reworked and lots of screws put into it. So I borrowed some tips from others here and scabbed together a melamine, MDF, and modeling clay mold.
Then I vacuum bagged a carbon, vinylester and nidacore layup. Gel coat down first. But I hurried and the gel coat hadn't cured enough so I got loads of print through. Then I forgot the breather material for the vacuum bag (doh!). So I got a dry laminate in the center under the vacuum port, so I had so re-wet the center with a wet layup and no vacuum and just peel ply.
But it came out ok in the end. Fairly light, but not nearly as light as if I was able to correctly bag it. It was 17 lb for the hatch which is about 63" x 27", plus gel coat.
I used aquarium "aragonite" as sandable anti-skid. $1 a pound at Petco, and a color match.
