If there isn't a circulation pump and you are concerned about whether or not the spa will freeze, rest assured that most models that don't have a circulation pump have a self-preservation mechanism that turns the pump on to cycle when the water drops below a certain temperature.
If you're in the Poconos, swing into the Hot Spring dealer there and ask for Bradley Marx. I believe he is still the sales manager there. Great guy from a reputable dealership. They're worth a look.