I am also in Central Michigan. I have an 8x16 wood She Shed I bought from the Amish. Hubby installed insulation in the walls and ceiling. Windows have storm windows he built, floor has laminate flooring. I have a ventless propane heater I run all winter. I turn it down to just keeping shed warm when I am not there. Usually around 50 degrees. I go thru a 40lb tank of propane every two and half weeks. Cost 20.00 to refill tank. I leave my stain, glue and all other freezables in my shed. By leaving the heat on my wood does not warp and my saws, drills and sanders stay rustfree.