Arizona advice:

In March, the North Rim of the Grand Canyon, and really all of Northern Arizona, can still have a large amount of snow. The North Rim will be closed until May 15, so if you choose the Zion and Sedona itinerary, the trip will need to circumnavigate the Canyon, either east along southern Utah through the Grand Staircase / Escalante National Monument, or along the west through the Hoover Dam to get to the South Rim. The western route along I-40 via Kingman to Williams is not very interesting driving, in my opinion.

I personally love the trip through the Zion tunnels and across the Escalante, as it is incredibly beautiful to look north up at the red cliffs, but it is a long way through Kanab to Page and down to the South Rim. Also, check the height of your RV, as the Zion tunnels have a maximum vehicle height limit.

The roads around Sedona have all been upgraded and improved in the last decade, so driving an RV aroung the Page Springs wineries, up the Oak Creek Canyon road, through Cornville to Cottonwood, etc. ought to be much less harrowing than it used to be. The Mingus Mountain and Yarnell Hill roads on either side of Prescott, however, are still narrow, twisty, and dangerous.

Summary for the Arizona route: Check your RV height to make sure you can get through the Zion tunnels, and take the route through southern Utah and around the eastern side of the Grand Canyon. Watch out for weather issues, in particular snow closures. Avoid taking an RV on 89A north of Prescott or on 89 south of Prescott. Do not exceed the speed limit in Wickenburg.