There are a lot more CGs than what you will find in the CG guides. Do a Google search for say "Marathon campgrounds" and then start calling especially the ones without web sites.
I am a fan of the Keys, but not Key West... too many fruits and nuts for my tastes. I do not recommend going to the keys the week before and after bike week at Daytona... way too much noise 24/7. Otherwise I would not worry about the crowds.