If you have a bigger RV and/or tent, I would recommend calling and having a note added to your reservation. Preferred sites do have the coquina/pea gravel pad for a tent. If your RV is larger (30ft or more), some sites may not fit a big tent and RV well.
Here are a couple of pics of my site (103) a few years ago. My 5er is 31 ft long. I had the rear wheels just onto the coquina pad with the trailer hanging over about half of the pad. There was room behind for a small tent, but it would have been tight. There are other Preferred sites with more room.