Very few organizers require roll bars for autocrossing. But it's a valid point. Check with them first.
You're going to find that you expend a lot of energy holding yourself in your seat through the corners. Angelwings Tech has the solution - Angel Pads. They fill the spaces between you, the door and the console so you don't need to be using your knees to brace yourself.
2-seater "Camaro" w/K&N cold air intake, oil cooler, Flowmaster exhaust, C6 Z51 brakes, Angelwings C5 Track Day Bar, Angel Pads!