I don't have a map in front of me to reference the campgrounds you mentioned, but two of my favorite civil war sites are just south of Gettysburg and kinda on the way to DC. The first is the Antietam battleground. It is the opposite of Gettysburg. There are few marble monuments and the battleground has been preserved much as it looked in the civil war days. It's very moving to get out and stroll through the fields and envision what happened there. The other place is Harper's Ferry, WV, just down the road south from Antietam. The town has been preserved so you can see what it looked like when John Brown attacked it. There is also an overlook over the confluence of two rivers that Thomas Jefferson described as the most beautiful sight in America. I've been there many times and don't get tired of seeing it. Hope you have a good trip.
Jerry