Quite a few coaches have some capability to add heat to the basement, often just one warm air duct down below that adds some heat whenever the furnace is running. Many are marginal, but the more expensive coaches may have more even heat or even a separate heat zone with a thermostat down there. I've also seen coaches (e.g. Monaco brand) that have a separate electric heater near the water bay that turns on when temps get near freezing. Heat pads under the water tanks are more common on trailers, but maybe some motorhomes offer them too.
Most Fleetwood models have at least some means of preventing a freeze in the basement area. Newmars too, I think.
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL