Minor update: I've gelcoated most of the cabin interior, and it has surprisingly helped A LOT with the outside heat thus far. Previously, it was unbearable past 90 degrees in the cabin, and now it's like being in the shade with the portholes open. I've decided to go ahead with insulating the cabin, starting with the ceiling. I'm using self-adhesive 3/8" mylar-faced PE closed-cell foam. If the self-adhesive begins to fail, I'll fix it with contact cement:
As a little experiment, I used some EVA decking foam around the base of the dinette seat boxes to cover the rough plywood. I want to see how well the self-adhesive sticks in a hot cabin on an uneven surface. I'm very pleased with the aesthetics:
Next, I didn't like the painted rough wood appearance of some of my head pieces, so I tried out some vinyl coverings. This stuff did not like uneven surfaces, so there are a few wrinkles I can live with.
For the sink top, I contact cemented 1/16" PVC sheeting under the vinyl covering. I originally wanted to used formica, but could not find any in small quantities.
I also hung the door to head: getting all the old screw holes to line up required some persuading of the shower pan