Ross did exactly what you suggest on his Panache with very nice results. I've included a link to his website.

: I cut out the fore and aft hatches for my strip-built boat. The question is,
: what have any of you done for the covers? I thought about flush, but I'm
: just not sure about how well they would seal. On my current CLC boat the
: hatches are not flush, but I really like the way they keep the water out.
: Aside from restripping the hatch covers, what else have others done? Using
: multiple layers of ash to build up the outside diameter of the hatches was
: a thought. I like the dimensions of the hatch openings themselves so as to
: allow plenty of opening to move gear in and out.

: Thanks for any ideas/suggestions.