I drain the water heater and use compressed air into the "city" connection to blow all the water out of the system. Make sure the fresh water tank is empty with valve left open. I have always left the faucets open. RV antifreeze in all the traps. Haven't had any issues in 10 years of owning campers. A lot of guys use the RV antifreeze pumped into the system which works great too. Hope this helps.
Todd & Kim
2016 3605 voltage
2013 RAM 2500 Cummins , RAM boxes, Laramie, crew cab
2011 RXV custom golf cart (Not for golf!)