The cabin top is done. I was able to remove the remaining drywall screws with a soldering iron and lots of patience. I then drilled out the holes and a few more and installed #10 bronze screws dipped in epoxy. I don't plan on ever removing these screws. I patched the screws and holes with thickened epoxy. Once that cured, I dressed down the sides of the cabin to make the plywood top flush with the sides. I noticed in some areas that the plywood did not fully attach to the side. So I used my japanese saw to roughen the slot between the top and side, then I filled it with thickened epoxy. Once that cured, I faired everything up and applied a seal coat of epoxy.
My next step is to cut the portholes and paint it. I've got to decide on how to mount the acrylic glass in the ovals so it's waterproof and looks pretty.