I don't know if the heat tape puts out enough energy to be useful - depends on how cold it gets and for how long, and how well you insulate.
If your tanks are exposed, what about the piping to/from them? They are more susceptible to freezing anyway (because of their smaller size) and more likely to break due to freeze expansion. Fittings and valves (especially check valves) are usually the danger point because the water in them can freeze up in a few hours whereas a tank may take 24 hours or more to develop much ice.
What sort of temperatures are you anticipating and how long a period below freezing?
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL