With our Arctic Fox, "winterizing" simply consists of keeping the thermostat above 40 degrees as long as the outside temperature is above 0 degrees F. The tanks won't freeze down to about -15F, but some of the PEX piping in various cavities will freeze (relatively harmlessly).
I would think that if you are keeping your small jugs of water from freezing, then the fresh water tank would not freeze either, with even a small amount of air circulation from the habited portion of the camper. If your waste tanks aren't heated, the place you need to be using propylene glycol (pink antifreeze) is in the grey and black tanks. If you allow them to freeze while moderately full, you could certainly crack them.