If you get just below freezing at night an above 40 in the day your tanks will be ok. Just keep a couple of gallons in them. It a mass to surface area thing
But your pipe an valves are another thing! Lots of surface area and a little bit of water that will cool quickly. Most of the piping is in side, but sealed off from your heat, in a cabinet or worse (like under the shower).
I had a TC where the CW line was directly below the opening for the electrical cord was shoved in (I could feel cold air coming in). And no insulation, bad plumbing layout to lessen the chance of freezing. This is where you need light bulbs for heat. Also check the area around the fill connections or pump cabinet.
Hope this gives you an idea what to look for.
