Pressure tank location
I had a similar situation. My wife and I bought a property with an old, poorly remodeled house and another newer house (mid-80s) with a shared well. I built a &quot;pump house&quot; that housed not only the pressure tank, but water softeners for both houses as well (no pun intended!). I also terminated various utilities (electric, phone, cable) at the pump house with a 200 amp generator transfer switch to supply one of the panels on my new home from the generator that was also housed just outsize the pump house. I call it my personal PUD!  The pump house is insulated and has never had any freezing issues (Western Washington State, so Pretty mild climate).   I'd suggest good insulation on your pump house and a small electric heater to keep temps over about 35 degrees. I think a gas heater would be overkill and more expensive than needed. A decent sized pressurized water tank holds a great deal of thermal mass and would likely keep the temps pretty even.  But if needed the electric could kick on for a bit to keep temps above freezing.