Thanks for all the advice it sounds like a much bigger job than I was hoping for, as it always is. I just had thought, but not sure if it would work. If the screws go into an aluminium plate in the hull, then is it possible just to keep screwing the screws into the hull so that they will eventually fall through to the other side and can then be taken out through the drain holes at the bottom? I suppose it's a long shot, but thought I'd ask.