No, you do not need AF in the FW tank. There is plenty of room for expansion. Did you run your pump dry? If not, you need to do that to get all the water out of it.
I'm not one willing to risk winterizing without AF. I blow out the lines, then pump in the AF (through my water pump). Does your trailer have a hose to suck in the AF through your pump? You can get a kit to install yourself if it doesn't.
RV antifreeze is rated down to -50* I think. I realize you are in a cold environment, but even getting down towards those temps, the AF turns to slush, not solid ice.
