Overcover helps hold in some heat and more than anything, in my opinion, shields you from wind. Whether or not you need one for 32F is an individual decision.
If you go with a SS put a space blanket on top of the OCF pad.
Since you're from MN you might want to consider an under quilt instead of the SS. Some of the less expensive ones, like the KAQ, don't cost too much more than the SS.