I am 66 and started working on boats and ships when I was 14. I am also a former union shipwright and commercial
fisherman. I have done dozens of decks in a variety of ways. I live on a wood former USCG patrol boat and have recently refiberglassed my decks.
For a long term seal, the problem is how much flex the seam must overcome. If the cabin
wasn't varnished, I would have rolled the cloth and resin up the panel an inch. Otherwise you need enough clean wood for epoxy to hold. That means cleaning
out the gap so enough epoxy is in contact with the cabin
. West also makes a flexible epoxy. I use it where metal hatches meet wood decks.
The fastest, easiest way is with an excellent flexible caulk with a trim strip embedded into the caulk.
Now I only use West epoxy and their 404 high density adhesive
filler. I don't use polyester resin for anything. A case in point, I used West epoxy and 404 to seal the tops of where my rubrails meet the planking and where sections of rubrail come together. The previous sealers weren't holding and this boat flexes in heavy weather
. In 4 years I haven't got a crack.