Last 2 years, we go down mid-October for a 3 day dirt bike trip. Still manage to sweat on the slower trails. We take my buddy's tent trailer (no A/C) and manage just fine. First year we ran a space heater in the trailer just to knock the chill, nothing last year.
Both times we stayed at the Slick Rock Campground on the north side of town. Nice campground but be prepared for bike/SxS/buggy traffic for all the people running the trails. Good campground with a lot of room though. Can be hard to get out of in the evenings when everybody is heading in to town for dinner (even hard for 2 street legal dirtbikes to get out of there). To be honest, we are going to start staying out in the desert for free from now on (less noise and crowds), but will be returning this October.