There are a few ways to get to Zion. Hwy 9 is very doable if your RV is within the maximum size and yours is. Many RVers do the drive and yes, beyond the tunnels is a curvy road for a short time. It depends on your comfort level.
I don't know what direction you're coming from but it appears you're from Virginia. If you're coming from I-40 to Flagstaff you can take AZ89 north to Page and west to Kanab and head south a few miles to Fredonia. You can also take 89A to Jacob Lake, AZ to Fredonia but you'll have another curvy hill to maneuver.
So from Fredonia you can take AZ389 which becomes UT59 taking you into Hurricane. It's an easy drive.
If coming from the north on UT89 (from Bryce Nat'l Park direction), take Hwy 20 a little north of Panguitch, UT over to I-15 and then I-15 south to Hwy 9 and Hurricane. Don't take Hwy 14 between UT89 and I-15. You won't like that one either. :)
It's nice to stay in Watchman campground in Zion or in Springdale, just outside the gate. Have a good trip!