If you happen to be passing through the D.C. area while RVing, and you intend to stop there during a holiday weekend, forget it. Your choices are minimal and it’s going to be ridiculously expensive.
We intended to pass through the D.C. area, in Virginia. Virtually every major campground was booked solid, or wanted us to camp for a 3-day minimum prepaid. For a 1 evening pass thru, they wanted $130 to $180. We ended up staying at a campground sort of off the beaten path for $40. It wasn’t great but it was only a 1 evening pass thru.
If you are military, get out your FamCamp book and look for a military base. I’ve stayed at three FamCamps. Every one of them was solid. I recommend them. I stayed on Andrews AFB in the FamCamp. I booked it 70 days in advance.