A few questions to get started. Depending on where you live, sub 0 means totally different things. Is that F or C? What is your average temp in the coldest and cloudiest month?
I'm guessing you could use
solar gain to protect a tank to about 5 degrees F below freezing but that's just a guess. Or maybe put it in a mock
greenhouse.
Water towers can manage very cold temperatures but they rely on a combination of a lot of groundwater "warming" them up and deliberate changes in water level to break the ice in them as it forms.