I use CA hinges and covering. All my surfaces are sealed (both sides) with Ultrakote. I dry fit everything as I go so my wing fits per, very good I would use foam tape if need be for sure. If you have a gap between the front of the wings and the fuse, build it up with some balsa sheeting/filler and then cover.

My servos fit nice, I believe I did have to trim a hair off the sheeting. If I go with floats I may look at a cover. Be sure to post pics of yours if you go that route. The only thing I don't like about a cover, it would not be flush with the wing surface!

Here is my progress, I'm just "winging" it