You're not allowed to bring folding chairs. People in the "prime" viewing location will probably stand most of the evenings. You may get some people sitting on the "grass" at the main stage between acts early in the evening before the "headliners". As you move further back from the stage, there are benches and other areas to sit down.
Remember, the core demographic of this event is Junior High and High School kids. To them, standing like that isn't a big deal.