When you say you sealed the rear vents, do you mean all of them? Keep in mind your blowers need to have a source of fresh air coming in so they can push the air in the bottom of the bilge out.
The two vents above my motors go in to the storage compartment under the rear seat so they do not let water in. I have the trunk transom, not the bumper holder transom. Are the vents on the bumper holder transom vented outside?
Water that ends up on top of the engine hatch should run into the lip around the outside edge, which goes out the scuppers on the sides. Water could find its way in from the vents on the gunwale or like someone else mentioned from the storage area in the transom (under back seat). Your cup holders (including the outside one if you have it like mine) drain into the engine compartment too.
Answers
Never had the engines get wet. I'd suspect a raw water leak from the engine for that.
PC BYC, Holland, MI
I agree with Handy, I've seen it come thru the vents and thru the back on several 342s and get the distributor wet each time.
Dream 'Inn III -- 2008 400 Express
2002 FV 342 on Lake St. Clair - Past Commodore SHC - Vessel Examiner USCGAUX
2002 FV 342 on Lake St. Clair - Past Commodore SHC - Vessel Examiner USCGAUX