Hi Eric,
Okay, I was kind of hoping that I would not be the only voice on this. Anyway, the logical jump to 48 volts was because I remembered you saying your array was 48 volts. In any case, (and someone who knows more than I about batteries may have some input as to whether this is a good idea or not), the SQF will not run on 12 vdc, it needs at least 36 vdc and 48 would be even better, so if in fact your array puts out 48 volts and you can run 4 12 volt batteries charging and running the well pump in series, but tapped in parallel to run your 12 vdc inverter, then that seems to me to be the best way to do this, in my mind just because that gets the inverter out of the well system and thus eliminates its losses and potential for failure, frees up the inverter for other tasks, etc. I'm not as proficient in battery system design as I am in water system design. Then again, switching 48 vdc may be a little harder to do than switching 110 ac. I'd have to look that up. Maybe someone here has some advice on that. You may want to just run it from the inverter, it's easy, and that is a plus. As far as the cistern vs. pressure tank question, you will have to bury a cistern and drain the lines to it etc. to achieve your frostproofing goals. In my area frost depth can be four feet not eight feet, but the same principles apply. Off the top of my head, if you want to frostproof the pressure tank system, you will bring a pitless adapter through the well casing at 8 feet below ground level and run, oh, at least about ten feet away from the well at that depth with your pump discharge line and put in a "stop and waste" valve. This valve will have a sleeve running up above ground to insert a tool into to turn it on and off and when it is turned off, it will drain everything that is sloped towards it downstream of it and let that water perk down into the ground below it. One caution about this arrangement. Never run the pump with that valve closed! From there you could run up to the surface and put your pressure tank there, drain it whenever you leave, and be in good shape. How you drain the cabin I do not know but figure you must have thought of that, and you'll have to do it either way. There are tons of variables in all of this, the well may run clear right away or it may need to be pumped with a kind of disposable centrifugal by the driller until it runs clear. The depth from which you must pump the well water, more than any other factor, will determine your options. Yes, you can, as I mentioned in an earlier post, run a regular submersible, and the smaller ones are available in 110 vac. If you're not lifting the water very far the efficiency penalty and inverter sizing needed to run the pump and its starting surge may not be big problems, but the deeper you go the bigger those problem will be. There are always six ways to skin the cat, and the best one is determined by way more information than I have about your situation, but you may also want to consider this, in my experience, the biggest complaint that people have with cistern/booster systems is actually the noise that the booster pump makes.
Hope any or all of this is useful,
Damian