Pull the drain plug/anode rod to drain the water heater.
Go to backside (inside the trailer), and actuate the water heater bypass valves.
Run the water pump a few seconds to clear out its little piece of line.
Attach air to city water connection.
Open low point drains and blow water out. Finger tight the caps back on.
Open each faucet (kitchen, bathroom, shower) and toilet to blow them clear.
Do the low point drains a second time for the fun of it.
Open all faucets.
Pour a little antifreeze down each drain, enough to fill the trap plus some to make it to the holding tank. Pour a little down the toilet.
Do this to mine every year, sees -20*F.