(so now you/ve shown us that you pre cut out most of the coaming, attach foam and layup glass, cut out the final pces and yr done)

so then why not exactly the same process for the flush hatches? partially cut out hatch, on underside of hatch area, mask out exact(or tiny bit larger for errors)hatch profile,mask around this 1 1/2" away all around so wood bare between, tempglue 1/4in or 1/8 in deep foam on inner masking, layup flange, cut out hatch, trim flange inner and outer(outer when real green to maskline), attach or mould in gasket.

same thing, same process,

as the foam(and therefore carbon/glass would have a 90 downturn(not the 45)) may even have some room to do all cuttingl of hatch later.