Keep it in a dry bag whenever the Zodiac is moving through spray or the weather turns, and deal with the salt the same day. Salt is worse than fresh water because the residue stays behind after the moisture evaporates. Back aboard, inspect the exterior, lift the salt with a cloth lightly dampened with fresh water, then dry it. Never pour water on the camera, and never grind dried salt across a lens.
Weather sealing helps and it does not make a camera waterproof or salt proof. A rain cover, a lens hood and an absorbent cloth do more for you in the moment.
Pay attention to the places salt collects: buttons, zoom rings, tripod feet, straps and zips.
For bags, the setup that works is a padded insert or compact camera bag inside a roll-top dry bag. You get impact protection and water protection, and it opens without spreading your kit across the Zodiac. Label it inside and out, because identical black dry bags are everywhere on an expedition ship.
Cold itself is rarely what breaks a camera. Moisture, salt, condensation and drops are.