You're going to love the trip
The RV park at monument valley is a little tight, but absolutely spectacular and not terribly expensive. South from Monument Valley, you'll get onto US 160 headed west toward Cameron. There's an RV park in Tuba City that I've never stayed at. Try to schedule lunch at Tsegi, in Tsegi Canyon. It's all good, but their Navajo Taco is outstanding. At Cameron, there's a small RV park across the road from the trading post. Few amenities, and sporadic reports of midnight noise. The Cameron trading post, as well as the one at Tuba City is worth a visit. There are several RV parks in Flagstaff. Black Bart's only has 20 amp and 50 amp hookups. I haven't stayed in Flagstaff in a long time.
I made this trip, from Phoenix as far as the LaSal Cutoff to Naturita, Colorado last September towing a 27 foot TT. The roads that you will be encountering will all be good. Watch your speed across the Navajo Reservation. Limits are enforced, and with good reason. The 15 mph school zones are enforced big time. If you are going south of Flagstaff, PM me for more local information.