When winter camping, I place a heater in the area of both the water, which is to the rear of the basement, and the waste tanks which are in the center of the basement.  I cycle that heater with a Thermocube.  It is a small device that looks all the world like a normal 110 volt splitter.  Instead, it turns on the heater at thirty-five degrees and off at forty-five.  It is available from many places, including Smarthome.

That worked but not well.  The tanks were normally warmer than they needed to be and I had to keep a close eye on power to the heaters.  I added freeze alerts and power them in the winter.  You can get them cheaply on Amazon.

I came up with something new.  I bored a four inch hole in the floor above the pump and hot water tank.  I bored another four inch hole on the other side of the tank.  I mounted a 110 volt muffin fan below the deck and wired that to the Thermocube.  I obtained the fan from a surplus house in Dayton, Ohio called MCM.  I then put a standard four inch duct grate over the hole.  Now when the temperature goes cold in the basement, the fan comes on and pumps air into the basement, across the pump, tank and piping and out the other hole.  Success!  The fan kept the water tank warm and I did not have to monitor a heater.
 

I then did the same with the waste tank compartment, adding a fan below deck that can suck air into the basement.  All you can see is in the picture.  Should I desire, I can close the grate.  I don't have to maintain and fuss over two basement heaters.

Works great!
 

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