follow up to my own post (still evolving my thoughts)might need to wrap heat tape around water jugs to keep from heating individual containers

Sounds like an expensive venture, but it might work. Only experimentation will tell. Mind you, experimentation has helped many of us overwinter tropical plants in cold climates.

Go to the Palms and Cycads forum and check out the way a poster named Artictropical overwinters great big palms in zone 4 Utah using styrofoam boxes and cfc lightbulbs for warmth. He has posted a lot of pictures on several threads. Extremely impressive. This method should be adaptable to a lot of plants and situations. The key to it seems to be the use of extremely thick, high R-value foamboard, sealed pretty tightly -- you can use a fairly low amount of heat as long as you trap it very efficiently.