RV Parks in or around Washington DC

Cherry Hill is the closest and most convenient to public transit (either take a bus from the front of the park to the Metro or drive to a nearby Metro station).

Otherwise, you can branch out in a variety of directions:
Washington DC Campground Roundup

I agree with others Cherry Hill is your best bet. Forget about "in" DC there are no CG's. The bus picks up right from Cherry Hill to subway and on to DC. You can leave your car with your coach and just use public transportation the whole time.

Cherry Hill X'3

Cherry Hill in College Park MD.

If you are retired military or eligible, Joint Base Andrews is a good place to stay to explore DC - and close to metro stations for the ride into town.

Rob

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25990622/gotomsg/25991125.cfm
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29191857/gotomsg/29192479.cfm
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29164234/gotomsg/29165040.cfm
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29138352/gotomsg/29139109.cfm
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29085571/gotomsg/29091512.cfm
etc...

Cherry Hill RV park is very nice, and within a few blocks of the Metro.