Thanks for the info. I am hoping for an early 2000's 2 stroke 150, but may end up going with a similar year 115. I have about $3000-$3500 for an engine and controls, so I may be pushing the limit trying to find a later model year 150.
While you have it open you could cut a hole in your core where the drain is going to go, (don't go through the outer skin) and form an oversized chopped glass and resin plug that would later be drilled out for the drain tube. That would ensure that no water would get in that way. You can also use the same trick for the engine mounts and 'ducer mount...