One old trick I did when I had a shop that I did not heat (as I live in Michigan as well) is I had an old refrigerator that did not work and I rigged the switch to keep the light on and I used an incandescent light bulb and it keep the glue and paint warm ware as not to freeze them and they could be used any time . I only cost pennies to leave the light on and old refrigerators can be gotten for free, and you can get a smaller one so it doesn't take up a lot of space and can be used for shelving for tools and other things that you would store in the shed as well heated or not. Or even a cooler with a light in it.