Questions about winter protection for a Trachy Fortunei

[palmmandan]

I just got my 7 foot in the ground last weekend. I live in southeast Michigan. The palm is facing south and protected from winter northern winds. I know I have 6 or 7 months to worry about protection but I want to have it all figured out before then. What is the most damaging to these palms in the winter? Really has not gotten below 0 here in my area last year. Usually 15 miles north where it becomes rural then it is colder. Anyway. I want to build something wodden like a box and lined with styrofoam on the inside. I was thinking about fabricating a plastic top so it gets light. Is getting light very important during the winter sleep?