I ran into this issue with my Georgetown class A few of years ago when I discovered that the plumbing compartment had no heat in it. The arctic pack heats the waste tanks and valves but, I believe, that's all because I've never found any wires to a heating pad on the fresh water tank. When we stayed at a campground where overnight temps dropped to 18F, another camper left his hydrant open and when the sun rose in the morning, had a lawn sprinkler from a (frozen) broken pipe feeding the hydrant. The campground manager said that with labor and parts, it was close to a $1000 repair.
I added a 300W gutter heating tape, attached to all of the pipes in the plumbing compartment, to prevent freezing. The tape came with its own thermostat and it's powered from shore power, the generator, or the 1kw inverter I had installed. The inverter gets used primarily when driving, when the engine alternator can provide up to 175A. Both of the low point drains were cut in the plumbing compartment and shutoff valves installed. This leaves the portion of the pipe that's exposed below the compartment dry and I don't have to worry about freezing. PEX tubing may take freezing without breaking but the pinch clamps that are used on fittings may loosen from freeze/thaw cycles. Remember, freezing water is what breaks rocks apart.