Sounds like skipping DC is non-negotiable but if you're going to stay in the area the best base from which to tour the area is probably Cherry Hill Park just off the Beltway on the north side. You can get a Metro bus to the nearest station or park at the Greenbelt Metro station and go in to town that way.
If you CAN bypass DC - find a way to get off of I-95 south of DC. South of Fredericksburg would be even better unless you would like to go through there at around 2 or 3 in the morning.
Then, head up in to PA via US Rt. 15 and spend a little time at Gettysburg, then continue north on 15 to Rt. 581 to I-83 north and then to I-81 north. From I-81 you can get to I-84 east to go in to New England.
Doug, Linda, Audrey (USN) & Andrew
2008 Sequoia SR-5, 5.7 L, 2000 Coachmen Futura 2790TB Bunkhouse, Dexter E-Z Flex Suspension, Reese W.D. Hitch/Dual Cam Sway Control, Prodigy Brake Controller, McKesh Mirrors
:B