I have an uninsulated shop where I ferment my lagers during the summer months. I use a side-by-side refrigerator-freezer in the shop for the actual fermentation. My problem occurs in the winter months when I can't keep the shop warm enough. Ultimately, I would do all my fermenting in the shop (ales and lagers) if it wasn't for the winter nights in southern Oregon dropping too low. What would be a cost effective way to maintain a mid 60s room temp during the winter months?