Last time my engine stopped it waited until we were half way down a narrow fairway between the pontoons /forums/images/graemlins/blush.gif.
Re CO detectors Tescos are doing them for about £5 at the moment.Friend of mine had his children airlifted off unconcious a few years ago due to a small diesel exhaust leak. They recovered thank God.
Tesco here I come. I guess I'm also lucky that the engine space doesn't communicate at all easily with any other part of the boat - at least not when all panels and floorboards are in place, so nothing noticeable leaked into the accommodation before the engine did a Jimi Hendrix.