For the cupola (the round hatch with the split-door), I wanted to have the doors overhang the outer ring just slightly for a better look (even gap/seam), and to provide a better seal. I put wax paper on the outer ring, then used thickened epoxy along the edges.
Then I remove the wax paper and now just needs some sanding. As you can see all the hinges are made of plywood, which has been glued on and thickened epoxy has been used to “weld” them along their edges. I will do this process on the edge of the oval hatch next also.