Storing Dahlia Bulbs
Well, the first thing is that they aren't really bulbs but in fact, they are tubers. Dig them, dry them in the sun for a day or two so the dirt can be brushed off. Don't wash them. Just put them into a cool, dry area. Keep them that way until you want to plant them next spring in pots or into the garden after frost.
It really is that simple. I note that heated basements aren't very good if they're kept warm. We're looking for 40-50 F temperatures in an ideal world.