If you are staying in DC, I would invest in either an Espar or similar diesel
heater. It uses the same fuel
as your boat so you don't need a secondary storage
facility. If you are passing through, a clay flower pot atop the stove or a portable propane
heater will suffice until you get farther south. Camping stores will have plenty of choices of heaters. If you are in a marina, you can use electric
until the cost kills you. Other than that there are few practical choices. Coal, wood, and renewable sources have severe limiting factors.
The best solution is to head
as far south as you can before the really cold weather