If you have space in the garage for them, just let them overwinter in the garage. Temps should not drop below freezing (32F) in the garage or wherever else you decide to store them (inside, greenhouse, dark closet, etc). The leaves drop off on their own. They do not require sunlight, grow lights or hardly any water (unless located near heat or air vents) when they are dormant (meaning when they have no foliage).
Here are instructions from the Plumeria Society:
https://theplumeriasociety.org...
