We don't drain down as we have a convector heater set on lowest setting and on a timer overnight to coincide with our economy seven electricity settings. Also leave all cupboard doors open so the "warmth" gets everywhere. Also leave the Truma water heater set on ECO and on its built-in timer. Never had any problems even in really freezing weather. Waste tank left open - disinfect it with a bleach solution before we set off anywhere.