From experience, you might struggle to find open sites. My suggestion is to plan out the trip as best you can and make reservations now. Worst case scenario you love one park and only get 3 days there or you hate one park and are stuck staying 3 days there.
Without reservations you could very well find yourself with no site and either Wallyworld camping or worse. Especially having a big rig, you are kind of limited.
Our first year going down to Florida we didn't have reservations until about a week out. We found one teeny spot (thank goodness for a 22 foot trailer at the time!!!) that was $110 A NIGHT!!! Now, it was a nice "resort" park with a nice pool and paver sites and very nice, clean bathrooms... but $110 A NIGHT!!!??? The next year we planned months in advance, found a spot half the distance from the water (less than half a mile) and about 1/3rd the price. Now that we have a 29 footer and traveling with the in-laws and require 2 spots (preferably next to each other, or at least close), we are having an even more difficult time.
Its possible, but anywhere nice in Florida in February is going to be busy. Finding a spot for a large camper makes it that much more difficult. Good luck and enjoy Florida!!! I think February is the best month to go. Its the coldest and snowiest in the northern mid-Atlantic, so those 70 degree days and 55 degree nights feel AMAZING!!!