Hello from the NC coast....Don't give up on the Keys ( State Parks ). We have been twice and both times reserved < 2 months out by getting cancellations. You just have to check often and be persistent. That being said we did make reservations this year 11 months out for the Christmas time frame because of specific plans to meet family and wanting a particular site selection. If you are a bit flexible with dates you may have a better chance. We never realized how popular the Keys were at Christmas.
On Savannah, we just came back yesterday and had a nice stay at Fort McCallister State Park. Large sites, about 10 miles off 95 at exit 90. Saw several deer, lots of birds, bunch of crazy racoons, and not many people.