You're probably safe this time of year around Panama City. While that area will be warmer than MI, you'll more than likely get freezing weather there throughout the winter. In January, there's no place in the lower 48 states that's completely safe from freezing so get as far south as you can.
Years ago, I was in Florida City (20 minutes from Key Largo on the Florida Keys) when I looked out the window one morning to see frost on the roof of my car. It doesn't happen often but it can happen. The past few years we'll gone west to Quartzsite for RV Week (the last full week in January) and then on to the Palm Springs area. It's been running 10 degrees cooler than what they call normal. This winter we're headed to Brownsville, TX to see how we like it there. We made our reservations 6 months ago for Jan-Feb & Mar at the same park - we don't usually spend more than a month at a time in a park but prices in south Texas are pretty reasonable compared to Palm Springs and south Florida.
Safe and Happy Travels!