Most Class A's that I'm aware of, leak a little heated air from the furnace into the water compartment. Others have heating pads for the tanks. But I've seen some manufacturers put them on top of the tank instead of underneath.
The water in the tank has thermal inertia...meaning it takes many nights of freezing temps to freeze it solid. And even longer if you park your RV so the tank side gets the sun most of the day. I've gone for weeks with 20°F nights and 40°F days. And several days/nights at 0°F nights and 20-30°F days. But when it got down to those temps, I'd put an electric heater in the bays. (Yes, a ceramic heater would work great). And left the under sink cabinet doors open. I also put in wireless thermostats so I could monitor temps near the tanks remotely.
If you don't have double paned windows, think about getting some insulating bubble foil to add a layer to them. And add winterizing pads to all the vents and the shower skylight.
It takes some work, but as long as the nights stay around 20°F +, and you get sunshine on the RV during the days, have a good source of LP for quick fill ups, and your electric is reliable, you'll be fine.