How big is your RV? Evidently you aren't towing a car?
If I remember correctly, there is a fairly large parking lot for Cathedral and a small RV could fit. You might try Googling the Sedona Visitor Center phone number and perhaps they can help.
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