The only places I would worry about.....
are at the joints. Seats joints could be under lots of stress and develop microscopic cracks in the finish which would be places of water entry. I wouldnt get real radical about it, but if you could find some flexible caulking to match your finish and caulk the seams so it wouldnt be noticable, do it.
Again, no need to get nutsy cokoo about it because even without the caulking, the seat will last a very long time. If you wanted to re-make it years from now, at least you have the pattern.
Have fun making it.
Tony B Retired woodworker, among other things.
"Strive for excellence and settle for completion" Tony B