For my water birds, I use either a thinned epxoy or Balsarite on the balsa BEFORE I cover my plane. The Balsarite is the better of the two. I also some times try to add a drain tube in the rear of the fuse. After I flying day or a submarine landing, I can just let the plane hang from the prop and the water will drain out of the tube. Be sure to wrap your receiver and battery in a good water "proof" baggie.