Yes, even being willing to book a FL Keys campground 11 months in advance doesn't guarantee you a site. We tried to book it one year but we were on the WEST coast at the time, so we had to both get up at 4:45 AM and get both smartphones, the ipad, and the computer ready to push the "book now" button at exactly 5 am. After trying for months, we were successful only once.
It was a lot of work because we had to look at and decide the night before which site to "go for" the next morning.
We then checked 2-4 times a day for Months, looking for cancelations. Got a few days that way, but overall? Not worth the hassle.
Sue