Here is the line of code from the AZ code causing all the bother.
17. "Light class motor vehicle" means a motor vehicle that uses use fuel on the highways in this state but excludes a road tractor, truck tractor, truck or passenger carrying vehicle having a declared gross vehicle weight of more than twenty-six thousand pounds or having more than two axles.
It can be found here under chapter 16 > Taxes > definitions 28-5601 item 17.
What it amounts too is RV were never taken into consideration and as such are included in the weight and axle requirement. So without an exclusion for RV's they would be included.
At first it looked like this article of the law might have been included under the commercial common carrier code but no they started a new section for the Taxes.
