Gulf Islands Seashore National Park is more than just Fort Pickens but this is an exceptional park. Located in the Florida panhandle near Pensacola, the fort is at the end of the island with the campground about one mile before that. You are right next to beautiful white sand beaches and you learn some American history. Here is a link: http://www.nps.gov%2Fguis%2Fplanyourvis ... oLa3GUwxdg
I also stayed at another facility in their group in Mississippi near Ocean Springs. Lots of wildlife at this one.