Hi, welcome to EBM!
I have had first a 29 and now a 31 moored at Elliott Bay docks for coming up on five winters now. Here is what I do. I do use my boat when weather permits in the winter.
I use an engine room heater to keep the engine from getting super cold. Here's the one I have :
It comes on at about 45 degrees and turns off at 55.
https://www.fisheriessupply.com/caframo ... 9510ca-bbx
I had Ranger install shutoff and drain valves for my cockpit shower and sink because they are quite vulnerable to freezing in cold snaps. This allows me to protect those fixtures and still continue to use the rest of the water system.
In the cabin, I use two of those round, low heat air dryers from West Marine. One goes just inside the "cave" while the other one sits on the forward stateroom bed.
https://www.westmarine.com/buy/west-mar ... ecordNum=1
I prop open the head door and also leave the cabinet doors open below the galley and head sinks.
I have a full canvas enclosure for the cockpit, so I leave a few upper zippers partially open so the cockpit doesn't get mildew.
I keep the fuel tank full to minimize condensation and add a biocide. I don't worry about the potable water tank or the holding tank because neither would be in danger of freezing.
That's it! Because my boat is in the salt water, which never freezes, there is no need to put antifreeeze in all of the water systems. The cabin and contents have stayed mildew free.