Hi Rob,
Last year, through the winter, I used golden rods for warming the engine compartment and a space heater and humidifier for the cabin on my R21-EC. I keep the R21-EC on its trailer next to the house and under a sunbrella cover.
To get power to the heaters I use a power cord from the house to the boat, then 3 extension cords branch to the shore power receptacle, the engine compartment through the fire extinguisher hole, and to the cabin through the anchor chain locker.
I checked the temperature of the engine compartment and cabin during a cold spell when the outside temperature was near 32F. With 2 of the 36 inch goldenrods inside the engine compartment the temperature was 52 F. The cabin temperature when using a Caframo dehumidifier and a Caframo space heater was 44F.
To monitor temperature I'm using 3 wireless temperature sensors made by Acurite which connect to my home wifi then to an android app on my phone. With the three sensors I can monitor temperature and humidity outside, in the engine compartment, and in the cabin.
During cold spells I'm checking engine compartment and cabin temperatures frequently.
I'm not sure about your batteries questions but I do keep the charger on at all times.
Hope this helps,
Bob
