You ever consider getting some heat mats to place under your pots?? It's something I do up here when I know my basement will drop below the mid-50's. I have them on a separate timer so that when the lights go out, the heat mats come on and keep the tent/grow box above 60F (~15C), and the root zone warm.. The ones I picked up are extremely low-draw, so I think at max the larger one was only using about 33w avg.. Plus, they're water proof, so you wouldn't have to worry about moving them in between waterings..