I have a Lance 1030. Running the heat while stopped keeps everything above freezing. My problem was running down the road in cold temps. I don't worry too much about the black and gray tanks since they slosh around and are flexible enough to not get damaged if they do freeze a little. My biggest problem was the fresh water pipes back to the bathroom.
Last winter I had one of those aha moments. I already had a 750 watt inverter to run/charge laptop computers. I found a 15 watt heat tape, ran it along the pipes inside the cabinets paying particular attention to where the shore water connection comes through the wall. While running, the alternator is keeping the battery up so plugging the heat tape into the inverter is really a no-lose situation. Haven't had a freeze up since. I've been in 10 deg F weather. Not sure I'd trust much colder though. YMMV