That's a great thought, and east coast vacation! Start in Virginia or South Carolina and head north! I haven't been back east in many long years now. Too cold in winter, just like you're having right now.
That's wild that you have to book so early on campsites, but that means there's a lot of demand. The smart man plans ahead and if there's no cancellation fee why not book up the two weeks and keep what you want nearer to the date.