In August, stay away from Bayside in Assateague. If there isn't much of a breeze the mosquitoes can be quite terrible. Oceanside almost always has a nice breeze in the evening (and can get quite windy) so the bugs are much less of a problem.
Consider Assateague State Park if you want electricity. But you will need to reserve as soon as reservations open; the electric sites book up very quickly. In either, the closer to the beach one is, the stronger the breeze.
I prefer the National Seashore over the state park if only because the beaches are less crowded as there are less campsites.
