yeah I agree Sept to Oct would be best, but if you want July and Aug it's doable. Just expect summer vacationer crowds and hot weather!
In MD assateague state park is a must stop, try to get a site in the sought after electric loop. (book as early as possible)
In NY, Letchworth State Park and Watkins Glen state parks were rated the top 10 in the USA. All said we enjoyed Watkins Glen better as Lots to do around scenic Seneca lake besides Watkins Glen Gorge. For Watkins Glen check out Clute Park Campground and Watkins Glen / Corning KOA, Letchworth SP check out The Ridge Campground
Also in NY, Cooperstown if your a baseball fan is a must. The Lake George area, maybe take a day trip to Ausible Chasm.
NH, Licoln/Woodstock area is a great home base and centrally located to exploring all of the White Mountain Attractions. Check out
Lincoln / Woodstock KOA, Fransted Family Campground
RI, Fisherman's Memorial Campground in Narragansett is another great homebase for exploring Newport RI & Mystic Seaport CT. Take the ferry down the street and visit scenic Block Island or enjoy the local beaches.
MA, Cape Cod is a must visit. I would strongly suggest booking just after Labor Day as traffic is just awful. Alantic Oaks Campground is at the halfway point up the cape and gets very good reviews. Watch out for the sharks while swimming! (I'm not Kidding as they have had problems)
ME. Acadia NP
VT, Our personal Favorite is Winhall Brook in South Londonderry, lots of country charm at the campground and in the area. Also suggest the Lake Champlain Area in VT, Champlain Adult Campground
Hope this helps!