Rule #1, NEVER trust shore power.
Rule #2 always winterize engine and head, drain water from tank, lines, and pump..
Rule #3 be sure that the bilge pump hose can not freeze after cycling and form an ice dam to prevent further pumping..
We almost lost a boat last winter due to rule #3, The bilge pump ran and did not pump the water out , ran the battery down, shore power, well, wasn't. Boat continued to fill up. Two of us went down and borrowed a AGM battery from another boat with a couple portable 1000 gpm bilge pumps. We contacted the owner and he showed up late in the afternoon after we pumped the water down to the floor boards...
Rule #4 Have an axillary portable bilge pump with long power cord and flex hose for emergency pumping. I like the little Rule 1000. We saved 2 boats to date from becoming submarines.
Rule #5 Have your friends phone numbers programmed in you cell phone in case you need help keeping your boat afloat.
Rule #6 Expect bibbing for years if you ever have to use Rule #5.
Cal 9.2 #19 SilverSwan