I just talked to the supervisor at Phoenix Arizona Department of Transportation. Recreational Vehicles no matter what weight are exempt. Only applys to commercial vehicles with a declared weight on their registration. The area supervisor went on to say we were exempt from truck scales and other commercial requirements. I forgot to ask about 3 axle RVs but would suggest you look at your vehicle registration to see if by chance it has a declared weight. The ADOT supervisor said they had never heard of an RV being ticketed, but possibly an over zealous enforcement officer could have. The supervisor said it should be dropped unless there is something else to the story.