Great Run!! I really enjoyed it last year.
Most folks parked vehicles at Gravelly Point Park, just north of National Airport; off of George Washington Parkway. I will not joke with you, navigating in that park on the trailer is hell. However, Mark House did it with his 37 AT, and TomCat did it with their 36 Skater. The ramp, is nice, but steep, so high tide helps; but low tide still stays 4 feet deep or so, just makes for a long ramp. The park is not locked at night, as people go in to watch the planes. It is supposed to be "closed at dusk", and being so close to the airport, there usually is a routine police presence in there. I have never had any problems parking in there, with my entire rig. Once in a while someone gets a busted tail-light, but that happens. The place gets really busy with picnicers and folks fishing during the summer, but this date will tend to make that die off I think. Entire park is free.
You can also launch in Woodbridge, VA, at Leesylvania State Park, where I always go. Tide also helps there, as it can get down to 3-4 feet shallow at low tide. Plenty of big boats go in there with no problems. You will have about a 25 minute cruise up river into DC. This park is locked at night. Launch is $8 bucks, and overnight fee is $5 bucks extra.
There are also several other places to launch. If you can get on base, Bolling Air Force base is very convenient. Ft. Belvoir and Quantico both have marianas down south. Ft. Washington Marina is not bad in Maryland. Pohick Bay Regional Park is not bad in Lorton, VA; but can get shallow at low tide. Occoquan Regional Park in Fairfax County, is not bad either, but has a long no wake zone down the Occoquan out to the Potomac; and curvy road to get there.
In DC, when going north to Georgetown by boat, anything north of the Memorial Bridge is no wake zone, all the way into Georgetown Harbor. Not a problem, just a pain. (Next to monuments and Kennedy Center.)
Dockage in Old Town for the party was no problem. Nicely done. Party and food was top knotch.