For Charleston, we stayed at Oak Plantation CG, southeast of town. Easier to get to than James Island IMO, and pretty nice. Older CG but lots of grass & trees. For Savannah, we stayed at the Savannah South KOA, which was fine, sites a little tight. Nice little pond & some (very) friendly ducks. They had tours into town from the CG. We'd go back to either place if in the area. I do recommend a city tour in Savannah, as you can learn some of the really interesting history of the city & the buildings you'll see. Ft. Pulaski is a really interesting spot to visit, outside Savannah.
If you are interested in the military, visit Patriot Point, on the north side of Charleston. And definitely visit the Battery (the old part of the city, along the harbor). Just park & walk - the place is just gorgeous. The story goes that Gen. Sherman found the city just too beautiful to destroy. I can believe it.
