If you have a 42 fiver, you can scratch the Federal Parks around Ocala off the list except Salt Springs. It used to be private so has big spaces and FHU. Keep checking reserveamerica you can probably get in.
There are many commercial parks you should be able to get into and get reservations. From there you can drive around and visit the springs, rent canoes, boats, pontoon boat on the St. Johns, etc.
ANother option is Silver River State Park. Big rig friendly and they are doing remodeling so are not taking reservations but if you drive up around noon you can almost always get a spot. Beautiful park and if you cant get in you can drive a few miles and camp in Wilderness RV Resort.
The following parks are all big rig friendly.
Williston Crossings in Williston near Gainesville.
Rockcrusher in Crystal River.
Carefree RV Resort Old Homosassa Springs
Wekiva Falls RV Resort in Sanford, near Orlando.
Stage Coach RV park near St. Augustine.
Ocean Grove RV resort St. Augustine.
Manatee Hammock (county park on the intracoastal waterway) Titusville east coast.
North Beach RV resort Villano Beach near St Augustine walk to ocean or ICW.
Ellie Rays RV Resort on the Suwannee River. Branford.
It dont get more old Florida that Branford.