Oh yes the Moki Dugway, have a look at this page. [You can find info on Bryce, Zion etc by scrolling through other pages back and forth.]
The tunnel in Zion really isn't a big problem and it is a spectacular drive. If you have any specific questions about RV'ing then ask away. If you want to share more details of your trip we might be able to make suggestions or help fine tune them.
Dave.
The Canyon overlook trail has very limited parking and you will be lucky to get an RV parked there. There is a bigger pull out further up the road at Checkaboard Mesa that might do but not sure how long the walk back would be.