In my M15 I was concerned, perhaps overly so, that in a capsise (last letter of alphabet key not working on my laptop lately), the enclosed area under the cockpit seats, would fill with water. So I purchased 10 cheap lightweight gym bags and filled each of them with about 10 empty plastic gatorade bottles, and fastened each bag closed and shoved them all under the cockpit seats, from the small access windows on each side of the companionway. It has the added benefit of filling up that area, such that anything that gets dropped in there by mistake, won't go too far so as to be virtually unretrievable, and it acts as sort of a stop wall for when i put small storage containers in there on each side. - Brad