I live in Ca and have done some research on this. As long as your conversion is a true motorhome, you will not have any problems. If you make it a toter and can still haul a semi trailer, then you will have to register as a commercial vehicle. All you need to do is schedule a vehicle inspection at DMV and if you have the necessities to call it a 'car house', then you will be ok. CHP does not do these types of inspections.
The problem is that a lot of truckers were trying to get a lower reg fee by registering as a MH and they were still hauling cargo, bypassing scales, etc.