Hi. Well, this isn't courtesy parking and it is further than you mentioned, but when we went to Edisto Island, SC last May, we stopped at a nice COE campground, I think it was in Virginia, or just into NC. It was a little bit of a drive off of I-77, but we liked it. A plus for us, which you are probably too young to enjoy, but we got it for 1/2 price since we have the Senior Pass.
While there we talked with the couple running the office and they told us a lot about work camping for government campgrounds and how to go about it.