Check the temperature of various parts of the basement, near the floor, as some places may be cooler than others. Sherpadog is right about not putting them right on the floor, as floors (esp concrete) sweat.

The lowest temp you can find that isn't below 45F is still better than room temperature. And you probably know that they need to be kept dry and protected from light, which will turn them green.

And don't store them anywhere near apples, as the ethylene gas they give off will cause the apples to spoil.

Sue