When I was IAD-based with TSA, I stayed in Frederick, MD with friends. You might want to consider something just inside the MD/VA state line. You take Rte. 7 to Leesburg, then US-15 north. The drawback to this is cars become a necessity. Another option, which requires cars, is Winchester, VA. Go west on I-66 or US-50 to get there.

Another poster said the public transportation around IAD isn't good and they're right. It never has been.

The Loudon County official who shut the crash pads down went to various apartment complexes in the area and looked for cars with out-of-state license plates. It seems avoiding Loudon County is the thing to do.