TexasH,
I will need to verify what I am getting ready to tell you with DH as my memory for what roads we have taken is really bad.
We did the Grand Canyon (Williams, AZ) to Zion area a few months ago in a 40' DP MH.
I believe we took 40 from Williams to Flagstaff and then 89 from Flagstaff through Kanab to Glendale, UT.
You go through an Indian reservations that has some beautiful scenery.
You will encounter grades - just keep the old RPM's up to cool the engine.
If you don't already have one, I would strongly suggest getting the "Mountain Directory West". It sure saved us on making wrong decisions on which road to take. It also allows you to prepare for grades you will encounter.
The area you are going to is beautiful and you will enjoy it.
I can't help you on the Zion Park CG. While in the area, you may want to visit Bryce Canyon and Cedar Breaks NM both of which I enjoyed more than Zion.
Also, between Kanab and Zion is a state park - Coral Pink Sands State Park - which has interesting coral pink sand dunes.
Enjoy your trip and let us know if you need help with any other information!!!
When DH gets back from shopping, I will verify that it was 89 we took.