You might try Hartge's in Deale, MD - you can lease a mooring for the summer, plenty of opportunities to work on your off-the-grid systems. In winter they move you to a slip - you really can't dinghy ashore when the creek is frozen
City of Annapolis has the same mooring-in-summer, slip-in-at winter deal at City Dock but I believe there's a waiting list. Both locations have commuter busses to downtown DC. You have to prove you've pumped your holding tank every (week? two weeks?) in Annapolis if you're anchored out, but they make it easy with a boat that comes to you for $5.
There's a 2 week limit on anchoring in the Potomac; I don't know how stringently its enforced. Good luck whatever you decide; we've been living aboard for 8 years, 7 of them in the Annapolis area, and loving the life.