Sorry to hear you had problems. I think your idea is reasonably sound, but I would recommend plugging the holes with epoxy putty first. When that sets up, do the end pours. The reason is, and probably why the original dams leaked, that that much epoxy gets really hot. It tends to melt/loosen the glue on masking tape. I had big problems because of this with the dams on my Terns. If you just taped over the outside and did the end pours, you could have a blowout all over the side of your boat. Not a pretty thought! The ideas mentioned earlier about using pipe are also very good and would be another alternative. Hope all comes out well in the end (pun intended :-)

Bill Price