Hmm, probably a lot of good options. Our green stuff here is pretty seasonal though, or at least the visibility improves a lot once the leaves are down. What time of year are you thinking?
In terms of areas that could support multi-session training camps, Prince William Forest comes to mind immediately (it really looks a lot like those training maps), and I bet the nearby Classic Champs will be pretty relevant. Probably hard to get in for extra training there or on the Marine Base's Combat Village maps.
The Hemlock Overlook / Fountainhead and Meadowood / Pohick Bay / Mason Neck areas are close by and will have lower visibility outside of winter, but may be slightly less relevant contour-wise.
You might also consider Little Bennet (not as feature-rich) or Elk Neck (DVOA?)
Some of our maps are very green but also thorny (Greenbelt?), which I'm guessing is less relevant in addition to highly unpleasant.
You can take a look through the QOC routegadget http://qocweb.org/routes/cgi-bin/reitti.pl
QOC gang- where else am I forgetting?
Definitely also consider the Atlanta area. A lot of the GAOC maps might actually be too open for your purposes, at least in the winter (GNC national event in January). But they might be able to suggest something relevant.