Hello Jerry & Char welcome to the Forum.
We stopped for a tour in DC a couple of Mos. ago. Had a wonderful time. The new WWII Memorial is fantastic.
We stayed in Front Royal VA, but we are members of Coast to Coast so we stayed at a members only park. But there are several RV Parks in that area. It's a great jumping off point to DC, Shenandoah Park, the Skyline Drive and many Historical Sites.
We Rode into DC on our Motorcycle, wouldn't do that again. Lots of reasons, ie. DC Traffic, Parking & Freeway jams. I would no doubt take the Train.
You can get all the info. you need about the train system at
www.vre.org You can park at one of the out lying stations ( the further out the better) and get off in DC. It's the only way to go.
Be prepaired to do a lot of walking. Almost all the Museums are free. You will spend a lot more energy than dollars.
Enjoy your trip. We sure did.