I grew up in DC & got outta that rat race back in the 70's. Been back a couple of times, & would suggest that you park at one of the suburban Metro stations ( subway )along I495 (Greenbelt station is a good one) & travel into DC that way. Head to Union Station & you will find several tours that start from there. Check out DC Ducks for a fun tour.
Check out Americamps in Ashland, VA. Great place to camp & staffed with friendly folks. Right across the interstate is McGeorge's Rolling Hills RV if you have any supply or service needs.
Have a great trip, & post photos! :B
