It's a nice campground, and you'll enjoy it.
Don't be surprised at their one time "gate fee" of $15 when you enter the park.
Be sure to use the correct entrance. Info from their welcome email message below:
In addition, please be aware that you will encounter a "low clearance underpass" with a minimum clearance of 12 feet if your GPS directions route you to the "West Gate" of Stone Mountain Park via James B. River/Memorial Drive. To avoid this low clearance underpass, you should enter the Park using the "East Gate" via Exit 8 on US78.
Fred