Camping at Wimbleball

Hi,
Does anyone who has done the race before know if it's OK to sleep in your vehicle in the parking field on Saturday night (bearing in mind that I have a camper van). I know the field is sloping but I can level the van. The campsite at the lake wants a minimum of 3 nights at £25 per night!!! I was planning on doing the van in the field thing but don't want to be turfed out in the night.
What has everyone else done in the past?
Nik

I haven't tried it to do it myself, however I do know that the security last year was pretty tight in every way up there - I wouldn't like to put odds on your chances of getting away with it..... I think if it were that easy quite a few would try to do it. Especially since it is pretty much in the middle of no where!