Many/most of the campgrounds in the Orlando area (Florida in general) are going to want a "deposit" or payment in full, when you make the reservation. Reservations are a two way street between the camper and the campground. Read the cancellation policies and decide if they can be lived with by the camper.
Orlando is Mouse country and most visited area in Florida by tourist. While there are a number of campgrounds that may meet the criteria outlined by the OP, I doubt too many of them will give a reservation without money changing hands subject to the cancellation policy.
We tend to stay ten or twelve times a year at either the Fort at WDW or at Tropical Palms (full pay up front) and did stay once at the KOA nearby once a year ago. None of these are going to meet the criteria outlined IMHO. Most visitors to Orlando, go for the entertainment in the area, Disney World, or one of the other great smaller theme parks in the area. When my wife and I are more interested in just hanging out, we will head down toward Everglades NP or on to the Keys (remote but in no way secluded though)
When our two daughters were attending college at UCF in Orlando, we would often stay in our RV, out east of Orlando at one of the many campsites, be it in the Coco area, Mims, Titusville, etc. and just drive our toad into to town to see the girls. This was before we moved to this side of the swamp and big lake. A number of years back, when we were full timing in our Class A, we spent a month at a CG in Christmas, FL, just east of Orlando, a ways. Enjoyed our stay there as well but don't remember any particulars about their reservation system and wanting money up front.
joe b.
Stuart Florida
Formerly of Colorado and Alaska
2016 Fleetwood Flair 31 B Class A w/bunks
www.picturetrail.com/jbpacooper
Alaska-Colorado and other Trips posted
"Without challenge, adventure is impossible".