I make a couple of winter cross country trips in my 2011 Georgetown 327DS and have never had an issue with freezing. I have, however, made some changes to the 3-season RV to make it more usable in the Winter. The lack of heat in the plumbing compartment was the first fix installed. A gutter heating strip zip tied to all of the plumbing lines with its own thermostat and an electrical outlet in the compartment provides a few hundred watts of heat. When we're driving, my post purchase installed 1kw inverter supplies the 300W the heating strip needs. The low point drains were modifed with shutoff valves inside the plumbing compartment which prevents freezing in the exposed portion of the pipes. The single pane windows are the next project, with bubble wrap covers for them.
I also discovered that the chassis ventilation system needs to be set to recirculate to shut off the outside air from entering the coach when parked. It enters through the recirculation vent but setting the system to recirculate prevents intrusion of outside air.
We also have a remote thermometer installed in the plumbing compartment. On a night with overnight temperatures in the mid teens, the plumbing compartment was at 40F, a reasonable temperature. I also do not use city water when it's cold. The internal tank is used and refilled on days when the temperature is above or close to freezing. This prevents hose problems and potential, very expensive, damage to an RV park's water hydrant. I saw the results of this a few years ago when another rv'er left the water turned on overnight and the hydrant pipe froze. He was very unhappy when the park owner said that he'd be responsible for the repair cost, approximately $1k!
Overnight stops during cold weather travel are made at RV parks with electrical hookups. I have a couple of electric space heaters that provide primary overnight heat for the coach with the propane furnace as additional heat when needed. It's also easier to keep the coach warm at night with the large living/dining slide closed. This cuts down the surface area for heat loss. Foam pads installed in the roof vents cut heat loss from them. I always keep the water heater turned on during cold temperatures. Heat loss through its insulation is part of the heat in the plumbing compartment in my rig.