Seabee and Steve are correct. I live in Westminster, MD and frequently travel the DC beltway. I have pulled my fifth wheel around DC to go south and back home many times but no more. It's no fun and no real gas stops that will fit a towed RV. It used to be there were slack times that you could gauge but not any more. Between totally discourteous drivers and sheer volume of vehicles, it's time consuming and white knuckle. And that's on a good day with no accidents. If there is an incident be prepared to sit, maybe even rent your bathroom facilities to other drivers in need
. While the alternate route mentioned above has a lot of stop and go from LaPlata to 695, it's far better than the DC Beltway. There is some work on the Potomac River Bridge that requires alternating lanes right now but are there are plenty of fuel stops. I recently found fuel cheaper in Virginia a few weeks ago so try and fill up there.
I avoid 95 and 495 even if it means going out of the way.
Now let me tell you how I REALLY feel about 95 and 495............