Depends on the time of year, during the snowbird season near the coast and south of Orlando can be tough. However you can make reservations 13 months ahead in Florida State parks so by making them now for next winter you can probably lock some slots in.
As for the Okeechobee area I doubt that is a hot spot but I live in North Florida so I could be wrong.
Off season it can be a good idea to have reservations in Florida State Parks for the more popular one, almost any on a coast for example. But if you get online with ReserveAmerica.com, put in a date and a general area you can look for sites that are open for that period.
Off season, commercial campgrounds often have open sites.
Arctic Fox 25Y Travel Trailer
2018 RAM 2500 6.7L 4WD shortbed
Straightline dual cam hitch
400W Solar with Victron controller
Superbumper