Interesting experience. I was curious to find out how are the nights at the camping sites, but I'm not brave enough to try to sleep there. And I hate drunk people.
You have just understood why most people try to find a room, either into an hotel or by someone who is local.
For example, if I need to go to the track, I walk 5 minutes to the tramway station, wait maybe 10 minutes for the next one and 15 minutes later, I'm on the Tertre rouge entrance.
I advise you to find a room next to a tramway stop next time, with a closed parking place:
http://www.setram.fr/
This way, you can park your car safely, enjoy the "parade des pilotes" the Friday evening and enjoy a nice week-end.
Samuel
(Not Heinz :D )