OK. After spending way too much time researching this I came across what I was looking for.
In the vehicle code, division 14.85 "Motor Carriers of Property Permit Act" section 34601
Sub section G:
(G) Vehicles never operated in commercial use, including motortrucks or two-axle truck tractors, with a gross vehicle weight rating of less than 26,001 pounds, when operated singly, or, when used to tow a camp trailer, trailer coach, fifth-wheel travel trailer, trailer designed to transport watercraft, or a utility trailer, never operated in commercial use. Vehicle combinations described in this subparagraph are not subject to Section 27900, 34501.12, or 34507.5.While this only addresses trailers (and not big trailers) and not TC's I think the spirit of the law is clear here. I believe this would be a 'leg to stand on' in court to fight a ticket. It also helps me rationalize declaring my truck as being operated at 10,001 pounds or less to avoid paying additional fees as anything over this amount would be strictly non-commercial and fall into the category of camp use.
Here is the section of CA lawIn any case it seems that mass confusion is the norm for citizen and government alike.