Balsa Wood Floor replace - Screw or Epoxy

[tpapenberg]

I purchased a Americcan Skier boat that has all the original floor in it. It consists of 1/2 ply wood and 3/8th Balsa wood on top of it. I want to replace a small part of the balsa wood that has a little rot. The 1/2 ply appears to be stained or treated with some rot resistant covering. There is no rot at all on the unerlaying 1/2 ply that I can see. My question is should I screw the new 3/8th ply to the 1/2 ply or use epoxy to glue the floor down? I don't want to trap water between decks but as it look like that is how it was designed and no issues with trapped water causing rot. (The rot came from a board edge on ski locker)