I am just using a very large water container filled with water with the lager in the middle to even out the temperature.
My garage is getting not much lower that 10oC at the moment so its thermal mass should be kept fairly constant.
I take it you are further north than me though.
I use the same thing for fermenting ales and the like but with an aquarium heater shoved in it to keep the temp at 20oC.
Cheap and cheerful at the moment.
