Are you looking specifically for campgrounds or a quick overnight?
You can do quick overnights in some rest areas, welcome centers, or walmarts. This is what we do from NY...never a campground. Oh wait, not true. We stop in Santee State Park in SC to summarize/unwinterize and get a walk in site. We have never had a problem finding a spot there although there are a few more campers on weekends. I think it is $19 during week and $21 (or close) on weekend. About 3 miles from route 95.
Our first choice is welcome centers because the parking lots are usually bigger. We take our knocks with truck noises.