We usually bypass Washington DC because of the traffic. I-76 to I-81 south to
I-64 toward Richmond VA to I-95 South. We prefer to stop at campgrounds each night. Truck stops are fairly safe (except for panhandlers) but they are also very noisy with truck coming in and leaving all night and lots of light in the parking area. Lots of people sleep in Walmart parking lots. Some do not allow overnight parking due to ordinances. Allstays has a list of Walmarts that do allow overnight parking: http://www.allstays.com/c/wal-mart-locations.htm We also arrive early before dark. Google Maps show 21 hours of driving. That's 7 hours a day which we think is way too many for us. We usually drive 4-5 hours a day plus stops to rest and fuel brings it to about 6 hours. If you do drive 7 hours, be sure to leave very early in the morning (6am) so you can arrive early. When we stay overnight I look up the location on Google Maps, earth view and zoom in to see the access and exit points and the size of the parking area.