We have a boat to worry about when freezing temps get here, and a well house..... and now a SMB!
For the boat we follow Jage's recommendation. We put an incandescant trouble light on top of the block next to the valve cover and close the engine cover. THis has worked for years. THe last winter we made it easier by adding little gadget that looks like a multi-plug. This little gadget acts like a thermostat, and when the temp gets to 35 it switches on the power. This means we don't have to leave the light on all the time or remember to turn it on when it needs to be on.
We also have a dehumidifier that we have tried to use with the boat in the spring anf fall when the floor gets wet, but it has never worked very well. We have not tried to use it strictly as a heater.
In the Well house we have a oil-filled electric radiator-style heater It has its own thermostat. The well house is a little more volume and the radiator works well.
I have not thought a lot about how we will keep McBeast warm on those chilly nights.
If we drain the fresh water and the grey water, what would the next concern be?
If we drain the fill line and the grey water, we might try using a pet heating pad to warm the fresh water tank.
...I guess I have more thinking to do...
Greg in Austin
2008 Ford 6.0PSD EB/E-PH SMB 4X4 Aluminess f/r bumpers (13.5mpg avg, 15mpg hwy) 52k miles [Texas McBeast]
2006 Toyota Prius (48 to 68 mpg) 120k miles [Penelope]
2013 Jeep Wrangler Unlimited Rubicon (15 to 18 mpg) [Johnnie]
2012 Mitsubishi MiEV (no gas required) ($.50/day in electricity) [Evie]