unless you are puting on at an odd hr - it can be pretty empty some weekends around then but still should be enough to arrange a shuttle. Weekdays can be a bigger problem as I've been there with no cars in the lot. Bring a bike just in case or rent one.
I've only hit it 2 weekends this summer and it was no at all crowded either weekend - not even that many rafts. The levels were good both weekends and there were not a lot of other rivers running. I don't know if it's the price of gas or lack of interest but it was nice.