Got the new cabin sides planed flush with the roof and sealed the seam with epoxy. While that was tacky, put on a layer of fiberglass tape with thin epoxy. This is the same construction that the hull chines have. I hope it is similarly waterproof. Well, thinking about that sentence, I really, really hope the hull chines are waterproof. That will be a much bigger issue than the roof if they aren't. This should strengthen the cabin significantly (although it already seems rock solid).

I also put a small backing strip on the joint in the cabin sidewalls to hold them aligned. I had sealed the side deck to cabin sidewall seam with a nice epoxy fillet. I don't know if I didn't get enough hardener in it or what. It seems to setting as things got warmer... maybe it was just too cold for it, but it didn't seem like it.

This led to my (not recommended) grass sidedeck feature.

I stepped in the tacky epoxy (of course) while working on the roof seam. Then I stepped in the grass. I thought I got it tracked off my shoe, but didn't. By the end of it all, I managed to get grass embedded on the port side deck.

That's going to take a bit more sanding.