Hamilton Jet Pump Hull Sealant

I am at a place in my project where I am ready to mount the jet drive to the hull. We are talking about the rectangular floor opening for the intake. Directions say smear sealant on both sides of rubber gasket.... question, what sealant? Don't want to use an adhesive sealant like 5200 because would be hard to break loose if I ever had to, looking for recommendations on a good bedding sealant, below water line.