At Gulf Shores, all sites that are available are open for you to choose. That said, if you arrive on a Sunday or Monday you have many more sites to choose from than on a Saturday. When you look at their reservation site, it will show you how many open sites they have for the day that you arrive; pick the best day.
Very few trees at GSSP since Hurricane Ivan came through in '04 taking out the trees and vegetation.
Great park; we hope to get back there in June.