hardware!
okay jk jk,
take some epoxy and mix in baby powder, fill the hole, and cover each side of the hole with the backside of scotch tape [non-sticky side] by cutting 2 peices of tape about 2" long, and sticking another peice of tape, sticky side to sticky side about 1/2" long in the middle of the larger peice- you now have 2 peices of tape which you can cover the hole with and the part of the tape that is touching the hole will be non-sticky [because it'll be the backside of the smaller peice]. this is incredibly strong, watertight, and is milky-white colored [im pretty sure you can paint it].
hope that wasnt too confusing, i know there are other ways but give that one a shot if you want it's simple cheap and effective.
Joe