Here's tool for checking out RV parks in every state. All you have to do once at the website click on the state you're interested in and it will give you a list of cities in that state. You'll be able to find all kinds of campgrounds in the specific areas you're looking.
http://www.rvparkreviews.com/I think you'll find plenty of RV parks with space available. When you get south of I-4 then you'll find some problems with extended stays. Remain flexible in where you go and how long you stay. The middle of the state, north or south, is better for finding availability.
We stay in Crystal River and our usual park, Rock Crusher Canyon, is usually very busy in February and March, but there are still vacancies for time to time. Check it out.