If you are thinking about Florida Keys state parks between November through April, the odds of getting a site without a reservation, is close to 0% success. The sites are of various sizes and if you reserve a site that is smaller than the recommended RV size (because you could not find the correct size for your RV) you will not be able to camp on it.
For camping in the Keys, you have to make your reservations online, 11 months prior to your expected stay. Odds are you still will be saying a few choice words because they are difficult to get even then.
We have best results by looking on line and checking for cancelled reservations. We have been lucky the last few years and have been able to get sites in December and January for 5 days. The problem is they were about 2 weeks before the opening dates.
But then there have been members that lucked out and got their reservations.
And we live in FL.
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329