We stayed at the Cherry Hill Park two years ago, and it was very nice. There is a bus stop at the campground; however, I would recommend driving to the College Park Metro station. I hope you have a great trip.
We stayed at Cherry Hill a couple years ago, very nice park. There is a metro bus station in the park that will take you to the train station. When we were there they had a daily presentation on how to use the bus/train and also sold tokens/passes. Sure made it easy for these first-time subway riders to get to DC and back. If they still have it, check out the "DC by Night" tour, picks up in the CG and a great guided tour of the DC sights.