The tank, waterline, elbow, hose heaters we've used have all been 120V.
The amount of wattage required would not be conducive to inverted / battery use alone.
Temperature and duration in the field would be a factor for you.
Many four-season trailers have enclosed insulated underbellies with ducting provided by the propane furnace (12V. blower). We've been in below zero conditions before without tanks or anything else being effected. Every coach is different. YMMV.
J & J
+ Kickr's the Vonderhund
, ES-38RSSA, 19.6K#
, 3500HD-Max, CC, 8'-DRW, 9.1K#