If it was me, I would go another 35 miles further south and go to Assateague National Seashore Park. The wild horses roam free. Oceanside drive in, loops 1 and 2, you can run your generator during the day, but they have quiet time overnight. You just walk over the dunes and you are on the beach.
Ocean City Sunfest is the weekend of Sept 19 - 22. Food, bands, crafts, etc - if you like that sort of thing.
Sunfest On Assateague, it's more laid back and quiet - very relaxing.
The National Park is $25 per night, no hookups. They do have water available, and a dump station. The State Park section has one or two loops with electric hookups. Not sure what the rates are in the state park section.