Know what I would do.
We only winterize once a year here on Lake Erie but have plans to move to Pamlico Sound some day. And I would worry about freezing temps since I watch the weather there religiously. So given those conditions I would add a 'T-valve' at a convenient location in the input water line but as close to the inlet seacock as possible. Whenever I left the boat I would put the free hose end from the 'T' into a container of pink anti-freeze and turn on the unit. When the pink stuff comes out the outlet thru-hull you should be protected. Or you can simply remove the hose from the seacock and, probably with an extension, put that into the container.
