Sorry..a typo on my part...I stated "I-15 south to UT50 at Hurricane, UT. It should have read "I-15 to UT9 to UT59 at Hurricane which becomes AZ389 into Fredonia, AZ".
Hwy 9 east of Zion is where the tunnels are.
If you don't want to go to Zion and you want to get to Page, AZ, I would suggest I-15 south in Utah to Hwy 20 just beyond Beaver to UT89 south to Panguitch and Kanab and then 89 into Page. (You could also work in Bryce Canyon Nat'l Park near Panguitch) However, beyond Page on Hwy 89 south the highway is closed and you will encounter a long, slow 25mph, rough (recently paved but done in a hurry to make this reservation road a detour so it's not smooth). It is doable, however. The detour will connect you once again to AZ Hwy 89 which you'd take into Flagstaff.
Another option is I-15 south to UT9 to UT59 at Hurricane, UT and continue on 59 which becomes AZ389 taking you to Fredonia, AZ. Then head north a few miles on AZ89 to AZ89 at Kanab, Utah. Take UT89 into Page, AZ and there you will take the above-mentioned detour.
If you still wanted to see Zion and Page you could easily do that from I-15, UT9 to Springdale. You could stay inside the park at Watchman c.g. or there are plenty of RV parks in Springdale, Virgin, Hurricane. If Springdale, the park's shuttle bus makes stops right in town to take you into the park - free. East of Springdale on Hwy 9 is where the Zion tunnels are so you don't have to drive through them. You would just backtrack a little on Hwy 9 west to Hurricane and pick up the 59/389 route into Fredonia. All the roads mentioned are just fine for your RV.
Look on a good AZ/UT map to get a feel of what you want to accomplish and what you want to see along the way. Good luck!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel