Our first trip to FL was in 2013 and we went pretty much without reservations and that was for February & March. Didn't have any problems finding a place to stay and even extended our stay in a couple of places.
I think the recession slowed down the flocking to warm areas a bit. The past couple of years has seen a resurgence in snowbirding. We settled in a park 3 years ago and while there are some vacancies they are getting few and far between. Fewer and fewer vacancies for reserving the next year out.
Hey, with climate change maybe the middle third of FL will become warmer. :) We prefer less traffic north of Tampa over the crowded areas in the south. There's plenty of warm weather and when it's a bit chilly it's nothing compared to shoveling snow back in Michigan. Maybe that's why we have so many Michiganders and Canadians in Crystal River.