I've discovered that with reserveamerica.com a lot depends on when a particular CG "releases" unused spaces. For example, I was trying to get into Bahia Honda in the Keys for just a couple of nights during high season, and I lucked out because one reservation cancellation occurred just minutes before I went on line. Similar thing happened at Oscar Scherer when they released six spaces at once. Of course, this was only in FL and I don't know if the same thing happens in other states using the same reservation system.