Best alternative to RV antifreeze.

Actually, you don't need to worry about the tanks. Unless they are completely full, there is plenty of room for expansion due to freezing. The lines, on the other hand, will easily freeze and break. Leaving the water dripping would keep the lines open unless it got really, really cold. Personally, we always just boogie south ASAP and choose travel dates when it isn't forecasted to be bitter cold. We usually blow out the water lines, put some RV antifreeze in the traps and don't use the toilet or shower until we get south of the freezing weather. Bottled water works for drinking, and can actually be used to flush the toilet should you have an _emergency" We use the fuel stops and the facilities where we overnight to take care of non emergency business. Unless you are driving from Nome Alaska, you can get out of the freezing weather in one or two days, tops.