Overnight camping in Delaware

Later this month we're camping in Frontiertown near Ocean City Md. Since it's more than a five hour ride from my home, we would like to go a day early and stay overnight and hope to have only an hour or so ride on our arrival day in Frontiertown. So far though, all the State parks have a two-night minimum. I know that there's a Walmart just about an hour away in Milford Delaware, and I have stayed overnight there years ago, but I'd prefer a real park of some sort. Any suggestions??