If I were leaving Michigan and heading south, I would "WING" it for one night until I got down far enough that I needed little/no additional heat.
You don't say what you are driving/pulling, but if your batteries are in good shape, they will last one night unless it is below 10 degrees.
Take extra blankets, hats, mittens that you can use JUST IN CASE. Warm the RV up, cut the thermostat back down and crawl in bed. Don't use up your battery with lights, TV, etc.
Next morning, run the thermostat back up, warm it up for your morning rituals, then get on the road.
Unless you are in the UP, you should be down in warmer weather by nightfall of the 2nd night.