I'm in SE Minnesota and inject whenever I can in the garage shop. I can heat with an electric heater to make life tolerable when its above zero, getting the shop temp to about 40 degrees. Below zero outside I fire up the propane heat until I get the shop to 60 then go to the electric heater to maintain tolerable temps. I do not store molds, injectors, plastic or colorants/component in the shop. I take everything I plan to use to the shop when the heat level is tolerable.
I have a pile of colors of plastic in the re-melt pile and will run out and melt a color or two for quickie shots and generally don't pay much attention to the shop temps to do those but can get some small bubble issues. I use these baits personally and pay no attention to the bubbles in the plastic.
By and large the temp in the garage is only important as far as your own comfort goes as long as the plastic and colorants are kept warm to eliminate bubbles.
