NC to Washington DC to Gettysburg Summer

I've stayed at Greenbelt NP, which is in Greenbelt, MD, just inside the beltway. It's about a half hour walk (at a decent pace) to the College Park metro station, depending on what part of the campground you're in, or probably a little quicker via bicycle. $16 per night without discounts, no hookups, not hard to get a site particularly when it's not peak season. When I was there the week of Thanksgiving, aside from the first night I could not see any other campers from my site, though there were a few others scattered about.