Four hours to mill the rough stock 4 square, an hour or so to mill the dados, another to cut the stub tenons, a couple of hours to size the panels, a...
I think the root of the problem is that the trim is pretty much completely exposed on the right side. You might consider replacing the quarter round...
I would use Unibond 800 over GG. Both are rigid and waterproof, but Unibond 800 has a very long open time, doesn't require high pressure, and is far...