We aren't laughing at cold times in Florida...However lows aren't that low and they don't last. Run the propane heat to the utility bay. That should be enough to keep the pump and lines flowing.
Know, don't guess...put a remote temp sensor in your water bay.Once you get an idea how the temp is holding in that area you can adjust your heat to suit you.
It takes a lot of cold to freeze a tank unless it is nearly empty. The pump and lines are more vulnerable. Keep your gray, black and fresh about 1/2 full as much as possible and you should have nothing to worry about. A full tank, if you had really bad weather may not freeze but if it did could crack the tank. So empty out the tanks in nice weather and only do a partial dump in cold. Cold spells down there don't last all season so you should get the hang of it ok.
Another vulnerable area is a kitchen sink on a slide. Check to be sure nothing is open or visible from the outside and you should be ok.
And, ice maker valves...if you have a plastic one, the vents on the back are all open, you have water pressure to that line and don't have heat going to that area...those valves are notorious for cracking even just a few degrees below freezing. Before we added heat and closed off vents we broke two of them. We don't use tank water ice so we just shut off the line and took out the valve.
Do not leave your dump valve for either of the waste tanks open during cold weather as a little ice can build up in the sewer hose &/or the valve. And don't leave a sink faucet dripping.
We do not leave the water supply faucet on when temps drop. Unhook to allow the faucet head to drain and drain out your fill hose then reattach when temps warm up.
Your cold spells should be short and fairly mild so just pay attention to details and everything will be fine...enjoy your winter!