While I'm not aware of any frequent Mainship issues, obviously any place on the upper deck that is getting wet and has fittings or other perforations can be a source during rain. Is the Flybridge covered/enclosed? Ensure the railing stanchions and mast base are properly bedded. Also, ensure the two upper deck drains are clear and flowing. I actually had the port side one plug up, and then, to make matters worse, the deck perforation between upper and lower fiberglass was not sealed. So water was running around the void spaces of the upper deck core!