In February 2013 we basically did the 6 week jump around Florida in our 5ver (much smaller than the OPer's). Did have state park reservations near Osprey (south of Sarasota) and 4 days at Knight's Key RV (just outside of Marathon) in the Keys. Other parks were usually reserved a few days ahead of our expected arrival. In fact, I think that is the method of "going without reservations." Keep yourself organized by having a plan or where you're going and when you plan to be there. You can always extend if sites area available.
Since our 2013 initial trip we've gone to 3 months and make reservations (usually at the same park). We've noticed a large increase in parks filling up, especially in February. Our usual park, Rock Crusher Canyon in Crystal River, was usually booked in February, especially on weekends and that's north of Tampa about 70 miles. You may want to make some reservations based upon general areas you want to visit. Leave some days in between reservations to roam a little, but you may find that calling ahead 3-4 days will give you some flexibility while insuring that you have a spot to camp.
Good luck!