I camped at the track during the Vintage Motorcycle races this year and had a great time (after camping at the Indy 500). What I saw was all dry camping at the Carousel corner. The weather was fine and I was in no need of electric. I don't know how many folks are traveling but water and wastewater should get you by for 3 days?
There are lots of great places to camp away from the track in the Kettle-Moraine and Lake Michigan areas. I was a tightwad and didn't want to pay the out of state fees. I was riding my motorcycle and met friends in the area. I stayed here
http://www.rvparkreviews.com/regions/wisconsin/west-bend/timber-trail-campgroundit was OK for my needs
I didn't think the race has been added to the Indycar schedule yet but I will say it's an awesome track and for sure, I would camp at the track.