I totally agree with choppercam. Unfortunately there really isn't any really great campgrounds in the Tampa or Orlando area, that aren't County or State parks. Fort Wilderness is the exception, of course.
This is only my opinion, but our family doesn't really care for the camping in a parking lot atmosphere. We have been spoiled by the County & State parks. Ft. Desoto is great, but you can only make reservations 1 month in advance, in person, and with cash. This policy is in place to give an advantage to the locals, who help subsidize the park. It is often full. If you will be there over a weekend, I definitely wouldn't take a chance on it. If you know someone in the area, maybe you could have them drive over for you. As for Hillsborough River, we drove through once when we were in the area just to check it out for future reference. Even though we love the private, secluded feel of camping, this was a little too much for us. It is veeery wooded. If I hadn't known where I was, I would have thought I was in the Everglades.
We haven't been camping there, because we were scared off by the drive through. Creepy crawlers aren't for me! If you don't mind the "parking lot" feel and are just looking for a pool and hot tub with a good location there are a few more options. In the meantime, maybe some Hills. Riv. SP fans can give us an update.