D&O No you do not need to and cannot book the camping (to my knowledge) but there is not a problem with space. Most campers are drive-ins rather than fly-ins. Just pitch the tents, and if you get charged, hard cheese. If you are lucky, you get free camping! Not a wives/girls campsite, however...
The general circuit tickets do not get sold out in my experience, but then I have always arrived on the Friday, and bought them "on the door" (rather than advance purchase) ...my guess is that they need the revenue so never run out!
Hope this helps...PM me if needs be.
DT