Actually, Balto -

There's a lot more than you think. The C & O Canal Trail gets you into some quiet territory very quickly. West of Harpers Ferry it gets really nice. And west of Hancock it gets sublime.

But there's more. Maryland has state wildlife management areas - many of which permit camping. While not exactly random - outside of hunting season, you are likely to be the only one there.
http://www.dnr.state.md.us/wildlife/allwmabyregion.asp

Same goes for Virginia and for Penna state forests.
http://www.dcnr.state.pa.us/forestry...Guidelines.pdf

Here are three:
MD - Deal Island on the Eastern Shore
http://www.dnr.state.md.us/publiclan...n/dealmap.html
(Call about the kayaker site on Broad Creek)
PENNA - Michaux State Forest
http://www.dcnr.state.pa.us/forestry...s/michaux.aspx
VA - Highland WMA
http://www.dgif.virginia.gov/wmas/detail.asp?pid=28