Terrarium/Aquarium heaters for chemistry?

After dragging my feet for a while I finally set up a darkroom in a room in my house. Throughout the summer it kept fairly even temps, but now that we are getting freezing overnight temperatures the room is incredibly cold. It's gotten to the point that it has been almost impossible to keep my chemicals at a consistent temperature when I'm developing. Has anyone tried using terrarium or aquarium heating pads to keep a consistent temperature?