coopec43 is correct, if brief.
OK. Your concern is corrosion
, and there are two ways to deal with that. One is a grounded anode which you undoubtedly have nearby. The other is keeping electrolite, in this case seawater, out of contact with the interface. Just about any isolating goo will do the job.
Choose one of high quality, such as with a high years claim, as in "30 year," but not 3M 5200 if you ever want to separate them again. Spread evenly, bolt into place, but do not tighten. Wait until after the stuff has set to torque it. That's important. If you tighten on wet goo, you just cut through it, and don't get any isolation or ability to push water
out, and the goo may loosen. Let it set, then do that last half turn, and you get a compressed gasket
. On to the next task in your haul out