Yes you should be able to stay overnight, there are always campers/RVs in the lot. I have not personally done this but the campers are always there by 8am when I arrive Sunday morning. I don't know about pricing, usually 40 bucks per vehicle for the day of. I will try to ask the attendants for more info about overnight camping when I go this Sunday for the Washington game. Hope this helped a little bit.
When I have gone early in the past it has always been open. I’ve arrived very early on Saturday morning several times for Sunday games. If no one is at the gate, you can just pay them the next day. I’ve always gone in an RV, but I’ve seen plenty of cars
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