Hilton head will have the most luxurious rv parks in the area. But it will be a drive to Savannah for the sights. Skidaway is decent, but I am not sure they have full hookups. Check out Tybee island, Rivers end campground. It is not a bad drive to downtown Savannah. There is a decent KOA in Richmond Hill GA, that is about a 25 - 30 min drive to downtown savannah. I know of several other places to stay, but few I would recommend.
We lived in Savannah for 8 years, loved every bit and we miss the area so much.