Need to warm wort in fridge

I bought a used fridge for the purpose of fermenting lagers at lower than Florida temps. I bought a Johnson temp controller and set everything up. We just started having a cold snap (35 - 45 deg F lows). The problem is the fridge internal temp drops to garage temp which is not much higher than outside temp. A beer I'm getting ready to make is using White Labs WLP833 liquid yeast. White labs lists optimum fermentation temp as 48 - 55. Since the fridge doesn't seem to have much insulating properties (since it reaches exterior temp internally) how do I keep the wort warm enough? Belts I've looked at don't allow extended operation time (more than 8 days). Since the fore casted temp range is 73 - 35 I need both heating and cooling depending on the day and time! Any suggestions? BTW, the beer is called Extreminator Doppelbock if that is important or will help.

Sounds like you need a temperature controller that can heat and cool. I'd look for the ranco etc with the dual phase. And a small heat source like a hair dryer (which is what I use).

I've also heard of heat bulbs for reptile cages being used for heating purposes. The don't give off light (except the slight glow) so they should be safe to use with carboys. When I build my ferm chamber I was thinking of trying them out.

I use a ranco dual with a 100w light bulb - works great. The ref. is like those in stores so it has a lot of area in there but the light does the job. You could just range a second johnson controller set to heat and us a light.

Good luck!