If at all possible, I would remove the softener and bring it inside where it will not freeze, and the brine tank also, as it will have water in it also. I'm not real sure I would introduce RV antifreeze into the softener, as I'm not sure what it would do to the media. Yes the attaching hoses need to be drained also. For the filter, just remove the can and remove the filter, and loosely reinstall the can. Be sure not to loose the O-ring for the filter can. If you have an air source, blow down the water system using the city water hook-up. Limit air pressure to 50 psi and open each valve inside and out, then the drains. Don't forget the hot water heater, and any water lines going to the refrigerator. Also the shower hose.