We are renting an RV in Phoenix for 9 days at the end of August. Our current itinerary is as follows: Sedona (1 night) Grand Canyon-South Rim (2 nights) Bryce Canyon (2 nights) Zion (2 nights) ...
I don't think you need 2 nights in Bryce, Zion the same, 1 night. Just not that much there for looking, relaxing yes.
Phoenix you could pick up Zoos' museums, etc if that interests you. Or maybe south could interest you; Kartchner Caverns - http://azstateparks.com/Parks/KACA/ 1 night You can go to Tombstone and pick up Bisbee and Tombstone - highly recommend this RV park - http://www.tombstonervparkandcampground.com/ Do the ghost tours we like the one that they drive you around.