I am going through that experience at this time. My port water tank on 1980 Morgan 41OI is leaking and I am considering how to to tear it out. Prior top removal We will saw a large hole in the top of the tank (13 by 28 inch hole is planned) and inspect the inside of the old tank. We know by the crystaline sand that comes out that the interior is corroding. I am looking for a fabricator of a flexible water tank of custom size and we will simply reline the old tank with such a custom bladder if we can have one made to exact size.