To the OP, we did discuss this at length and the problem is you apparently have people in high places in AZ who do not know how to read or interpret laws. A motorhome is not listed in the law. The law applies to "passenger carrying vehicles" or the listed trucks. A passenger carrying vehicle is a term used to describe vehicles designed to carry passengers for hire, such as a bus.
And the issue is more than just pay the tax. There are only 76 commercial fueling locations in AZ. So if you think you need to pay the tax, you have to go to one of those 76 truck stops to buy your fuel. You can't pull into the local AM/PM and fill up with their diesel.