In 45 years in the Salish Sea, Anacortes and Olympia, I've never had a line freeze. A couple of West heaters at their lowest setting pointed at higher-risk plumbing have worked.
The biggest problem in this region during the winter is mildew. A good dehumidifier draining into the galley sink and good air circulation into all corners of the boat is critical.
One thing to watch out for is the electrical system of your marina. With every heater in the marina coming on during a cold snap, many marinas don't have adequate service. For insurance, a cheap weather station connected to the internet can let you monitor the temperature on the boat and give you a warning that the power is off.[/QUOTE
ye may be simply lucky. I live in Gibsons and we get COLD blasts down Howe Sound. Same can happen from Indian Arm, a branch of Burrard Inlet and down the Fraser River valley.
If you have inlets aimed at you or nearby be a little more cautious since they are often the sources of the very cold air that hits many areas.
I may have gone overboard but for many years travelled south in our RV so the boat had to be prepared for a winter alone. I had a friend check it but I did not want him to need to do more than minor stuff.
I drained the water tanks, the hot water tank, the supply hoses for the drinking water system. No pink AF though.
I set up a 1,000W heater in the engine compartment that was controlled by a 3,000W thermostat for baseboard heaters laid in the saloon above. Hatch left open. THermostat set for about 4-5oC.
I also leave one 75W heater under the V berth platform and in the lazarette for a small amount of heat.
I use about 20 small muffin or computer type fans mounted on small boards so they force circulation all around the saloon, V berth, eng compartment,
head, lazarette THey only draw about 10Watts each so even the 20 use about 2 amps. THis way I can aim them to ventilate specific areas that proved to be troublesome.
THe cushions, all of them, are laid down flat with 1x2 sticks, each cling wrap wrapped and ends taped, between each so they get some air movement between. THey are pulled away from the walls.
The V berth cushions are raised on old planters, CLEANED, so there is air space.
Almost forgot the two small dehumidifers left on a timer so they did not run 24 hr a day. Usually about 4-5 hrs. One draining to the galley sink, one to the head sink. I modified the collection tank with a small piece of tubing long enough to reach. Each hole was pilot drilled and then enlarged running the bit backwards so to not grab and break the tank. Checked the tube fit each time untill I could just force it into the hole.
The engine coolant is AF and checked.
The raw water circuit is pink AF treated for protection.
All the pumps, FW, bilge are pink RV AF treated.
The toilet and the holding tank and its pump is also pink AF treated.
Batteries were fully charged, voltage noted the day before we left , charger disconnected and then the voltage checked when we returned. THe voltage loss was minimal, about 0.3 V , well within its full charge range.
Of course since I became a home body, no more travel, I can get down to the boat almost any time I wish and I do so, so nothing is likely to go amiss for long. But I still do it all.
Pick out what you wish. If you are able and willing to visit often you likely can get away with less preparation but just monitor the boat often.
