The Madeline Island Airport (off the Wisconsin shore of Lake Superior) has a great on airport campground. You can also get scooters, bikes, and mopeds to rent for CHEAP while you are there.
There is also a State Park for camping and a National Park.
The town of La Pointe is 1.5 miles from the airport. The rental places as well as some restaurants will come to the airport and pick you up and take you into town.
Michael
PS: Just saw you were looking for SOUTHERN US. Well, Madeline Island IS on the south shore of Lake Superior!