I would say it's going to be very crowded...it is peak autumn colors and great weather, plus many visitors to Zion this time of year. Best to get there before Friday or early Friday if possible. Several marked sites, and several open areas with dispersed camping, but betting that all will be full for the weekend. There is more dispersed camping heading to Zion...turnoff is on the left a few miles from Sheep Bridge...I forget the name, but it should be listed on Campendium.