I'm going to try and overwinter some crops this fall as well. I wasn't thinking of spinach but your post is making me think. I was thinking of doing garlic which I've read will be fine in the winter. I'm further south than you in North Carolina, so hopefully it will work out.
You should be fine down there so give it a try. Garlic really needs to be planted in the fall for a harvest the next summer - even north of me.