Time of year - Weather wise and water temp wise it is a great time. The days are a little short then so its harder to paddle big miles.
From Havre de Grace to Elk neck is no problem,only about 7 miles however. The campground at Elk Neck is not near the boat access area.
The entire western shore from just south of Havre de Grace to the Gunpowder river is off limits - US Army artillery range and secret testing area for artillery.
On the eastern shore there is a place to camp about 25 to 30 miles from Havre de Grac across from Pooles Island. Pooles Island is still part of Aberdeen proving ground and is patrolled. I suspect there is one or two spots near the mouth of the Sassafras about half way between havre de Grace and Pooles Island.
Back on the Eastern shore there is a campground on Hart Miller Island and another on Paradise Island just south of there.
There are some small stealth areas just north of Rock Hall on the other side of the Bay.
Next down stream there is a little used new park just south of the Bay Bridge on the western shore. Probably could get away with camping there if stop late and leave early.
There is nothing available on Kent Island.
There are some sites along the shore of the mainland north of Tilghman Island.
You can probably get away with staying on Coaches Island which is private. You won't have much luck on Poplar and will get hassled because it is still under construction and is a turtle breeding area.
James Island is the next available spot. Very nice.
After that there are plenty of places to stay if you can find one that stays above water during high tide.
Plenty of places to camp on the Virginia Penninsula from the border on down.