Wouldn't fancy pitching a tent there myself. The area round the central henge is quite exposed being close to the road and a tent might attract the attention of any passing idiots or police late at night. There's a bit of parking space next to the nothern henge iirc, might be nice to spent the night in the van there but I don't know if there's any room for a tent. It's been a long time since I was there last so things could have changed re access. It's your call matey, I don't want to put you off :-)

-Chris