Winter Drain Down
When draining down the water system for the winter don't forget to open all taps at the sinks in the bathroom and kitchen area to allow the water to drain out of the pipes. It is essential that in addition to emptying the holding tank you also drain the water heater.
If your bathroom has a shower it is a good idea to remove the shower head as any water remaining in it could freeze and cause damage.
Finally when the system has drained I would suggest you go for a short ride in the vehicle with the drain taps still open, the movement will encourage the last drop of water out of the system.