Thanks for your input, much appreciated! Those sound like some very similar situations.
That's been my method too, no watering before/during a cold spell. Winter low temps here just depend on which way the wind is blowing. Some nights are in the high 40's, or there could be an ice storm, and quite a bit of rain is normal. Last winter was so mild that many plants that got frost-bitten foliage survived at the roots and have grown back so that they look fine, but would just never have a hope of getting to a mature size that way, and an unusually mild winter is not something to "bank on."
In a garage, shed, unheated GH, the temp might get as cold as outside the structure, but dew doesn't get on plants, therefore there's no actual frost on them. That seems to make a difference, from my casual observation.
Since I have at least 2 of about everything, I'm planning to have at least 1 of everything "important" in the house.
I've realized I'm only considering plants with origins in dry climates as candidates to use the GH space, vs. jungle epiphytes. Is that a consideration others use if faced with similar options?