Some good advice and some questionable.
First PLEASE do not use auto antifreeze, this is not designed for that and is in fact poison where RV is not. You can also get in trouble dumping this in sewer systems.
Also do not use salt, if you want to promote corrosion go ahead but adding high amounts of salt is asking for difficulties and again is not good for the environment or sewer/septic systems.
If you are not sure of what way to go then stay winterized and use RV antifreeze to flush. I use the large water jugs with pumps on the top for really cold weather so I don't need to worry about water lines freezing.
When you are traveling a night of cold will not hurt anything (reasonable cold, not -35), pipes don't burst from one cold night. Several nights of cold with only slight warming during the day can hurt things as freezing and thawing will create blocks in the pipes then when they freeze again the water has no place to expand and will blow a pipe. I leave my units with water in them till late in the fall and they freeze a number of times but fully thaw during the day as I run the heat or the outside temps are warm enough.
One trick is to shut your water pump off and open the taps if you think it will freeze at night, also leave the hot water heater on if you have water in it.
Or if you are worried open the inside taps and the low point drain in the morning and by night the lines will be pretty much drained *** IN MANY CASES THIS WILL ALSO DRAIN YOUR HOT WATER TANK DOING THIS SO DO NOT TURN THE WATER TANK ON ***