Just been looking at Hell, shame that I don't have more time off work/live closer to Gatwick as it seems quite simple to do. A 8pm flight on Friday night to Trondheim, rent a tiny car for 3 days (about £50 a day) to cover the short drive to the track (think you could do it on bus/walking if you arrived a bit earlier), pay £90 or so for camping, £45 for camping and you're done. Not a cheap weekend, but if you can do it with a few of you then the car hire/camping can be split.