... we live just west of Minneapolis... we will head south, destination not yet decided, the first or second week in December...
To avoid snow you need to leave about the middle of October. After that you are at the mercy of Mother Nature. As you know you'll have to be winterized and won't be able to un-winterize till somewhere in southern Missouri.
...for about 3 months. Thinking south Texas, Mississippi, or Alabama, or spending time in all three.
Thinking you're going to find it a little cold in Mississippi and Alabama. There are many snowbirds that do go there (south of I10) for those months, but be prepared for frozen water hoses. For Texas you'll need to be south of Dallas/Ft. Worth. Even in Hill country you'll get frozen water hoses. A couple of hundred miles further south and you'll be fine.
My general rule of thumb is for the months of Jan/Feb you need to be somewhere between I10 and the boarder or salt water.
Good luck on your first snowbird adventure.