Flexible steel hose is the only thing I've ever seen anyone vent auto exhaust with. Seems like an awful lot of trouble. Besides, vent it where? You'd have to have a sturdy pole if you are venting it skywards to prevent a scorching hot hose from falling on someone or their car. How about leaving your car off till you're ready to leave instead?
Just turn your car on when the people around you aren't there. We ran our car at least once or twice a day when no one was around and it was no big deal. We were on the end though so we only had to worry about people on each side of us - we weren't in a middle of sea of tents so it might be a bit different in that case. Or talk to your neighbors and you guys run it at the same time. Just don't be rude and do it while everyone is sitting and hanging out.