There aren't any legal places to wheel in "Northern VA" but if you go west to George Washington National Forest (GWNF) around Harrisonburg and south, there are numerous opportunities to wheel on public land. Keep the Tread Lightly principles foremost in mind and practice if you want these trails to remain open.
That said, Welcome aboard and enjoy the sport. Feel free to PM me fi you would like some particulars about GWNF wheeling. A buddy and I are in the midst of doing some exploration for more trails that aren't too far away to do in a day trip. We had great success Sunday and plan to do more in the coming weeks. We will post here directions and trail ride tails (pics too if we stop wheeling long enought o pull out a camera) when get a few details irinned out.
Another thing you might try that will really help is to call the rangers at the district office that you may want to visit and tell them you are looking for open "Jeep" trails. I did that last week and got point to point directions from the helpful rangers on duty.
Good luck and happy wheeling.