By "lower elevation", do you mean higher than the greater Phx area but lower than Flagstaff?
There are quite a few RV parks in the Verde Valley....Rancho Sedona, Dead Horse Ranch State Park, Distant Drums, Rain Spirit, Thousand Trails, and more.
Try checking www.campgroundreviews.com (used to be RVparkreviews)
There is boondocking available off the road to Thousand Trails, which is off Hwy 260 between Camp Verde and Cottonwood. Also boondocking on FR 525 which is off Hwy 89A between Sedona and Cottonwood.
Hope this helps.
2002 Itasca Suncruiser 32V
2012 Suzuki Grand Vitara