I'd ask around at nurseries or among other dahlia growers, as you likely have already. If you have enough plants to run an experiment, why not lift some dahlias and mulch others for a little hibernation underground? I've had them survive in the ground in our freezing winters and feet of rainfall, so they can probably take whatever Dallas winters dish out.

Good luck!

Running an experiment like Poochella suggests might be fun to try but you can lose tubers bringing them inside just as easy as outside if you don't take the correct precautions. I would just mulch them good 6"-8" of leaves or whatever you use to mulch. That should hold them for the winter and then if you want to divide them dig them up in early April and eyes will be showing and divide one eye with at least one tuber and replant when the soil is 70 degrees. Hold until that time in plastic grocery bags to keep the air from drying them out.

I talked to a grower from Ohio a few years ago that kept his tubers in the ground all winter using a cover of leaves about 18" thick to keep them from freezing.

Check out the DS of Georgia newsletters at our website for growing dahlias in the South.

Here is a link that might be useful: Dahlia Society of Georgia