Go via the main entrance, through the booths, go straight on past the hospitality suites and turn left just before the toilet block/go kart track, you will probably see assorted tents, caravans and motorhomes on your right hand side as you go up there
I believe the camp site that Bryan mentioned is the marshalls campsite which is normally only used at big meetings BTCC etc.
Will be there myself at some point on Friday so see you there
Steve