You're right. It is Glen Canyon National Recreation area.
However, I am going to Zion through the east entrance Zion-Mount Carmel Tunnel via Route 89 and 9 from Kanab, so it is only 28 miles from Kanab. There is a $15 fee for a motorhome going through the tunnel, but it is such a beautiful drive, and I have gone in that way several times in the past and know my vehicle fits.