I have gone to Zion the first week in November the past 4 years now. I try to get there for their annual Plein Air event
. The weather is usually beautiful. Not too hot, like summer can be. It can get chilly at night, and it's possible to get a quick storm. Last year it rained off and on for two days, then it cleared up and was amazing.
I think you will find the park less crowded, cooler and completely enjoyable. You might still want to check out reservations for camping, only because they close down sections of the campgrounds in the fall and winter, so there are fewer total spots.
Salt Lake City