Our rig is sitting outside with RV antifreeze in it, but this is the last year.
I have a blow out plug and will be using that. RV antifreeze still goes in the drains though and a bit into the gray and black tanks to keep the dump valves from freezing shut.
Don't forget to drain the fresh water tank with the spigot and then run the water pump dry before you blow out the lines. There is a check valve in there that will keep water in the pump if you don't) the pump could be damaged if it hard freezes.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW