We use the coach in winter too. I don't drain and re-fill as to the need. The coach has (2) electric bay heaters on thermostats set for about 35-40 deg. I installed a schraeder valve and some ball valves to bypass pump, HW tanks, etc. I place a stick holding open the toilet foot valve, open all the faucets and set my airs psi to about 40 and blow both HW and cold lines out. I've not had a problem in the 3 years I've done it. When I need to use the coach, usually within the week ... it's ready fairly quickly.
Jerry H.