one of my bays has a 100 gallon water tank and the bay next to it has a large opening with the 65 gallon black and 65 gallon grey tanks. I plug a small 120 volt heater into one of the temperature activated plugs which activate the heater when the temp in the bays gets down to 35 degrees. I have been in temps down to 10 degrees for 2/3 days and never had any freezing problems.It doesn't matter whether I am plugged in or on the generator. If I am plugged into a campground using pole power then I run a separate power line from the pole power stanchion to reduce the load in the RV because I run other 1,500 watt heaters.