This is the one I used on my 18SF.
Jim Black 7x14
http://greatlakesskipper.com/jim-bla...oat-deck-hatch
Has a neoprene seal.
Worked great the first 3 years or so, but the oil/gas/mung that drips out of my old two stroke has started to break it down a bit and now it leaks.
Need to replace the seal.