There really isn't any ambiguity or wiggle room here: CC with a utility box or flatbed has to stop at scales in California. Sure you can get away many times just bypassing them - as you can in a box truck or even a big truck. But it is illegal. It isn't just the inconvenience of getting pulled over, in California bypassing the scales when you are legally required to stop is a criminal offense, a misdemeanor. Are they going to arrest you? probably not, but they could.
There is some ambiguity on the new pickups - they do not meet the 11,500 GVWR limit for "Pickups" as defined in the CVC. If registered as other than a pickup body type, you will need weight stickers and have to (legally) stop at scales.
You can register most anything as a passenger car or RV, but in either case if you are caught with something else in the bed - it does not need to be commercial use, just hauling some 2x4s back from Home Depot - you are technically in violation of your license.
I went through this with my newer stock dually with pickup bed. 14,000 GVWR is listed on the door and the initial registration done by the dealer was body type "Commercial other" which is about the only thing that fit the letter of the law. The plates came with weight stickers and the law said I had to stop at scales. I spent 3 days at the DMV over about 5 months and got it changed to body type "Pickup". Now I don't have to stop at scales or put weight stickers on the door, but I might be in technical violation if I ever weigh more than 11,500 with something other than the camper in the bed. Even that could be argued: in the CVC a camper is a load in a pickup, in the Health and Safety code its an RV.
I have researched this extensively and have all the relevant CVC sections at my fingertips. CC with utility bodies have always had to stop at scales, it has just been weakly enforced. The problem with the newer pickups exceeding 11,500 GVWR is new, and the CVC hasn't caught up with it.
I really wanted to do a utility body on my truck but all this convinced me that it is impractical in California. You can continue to hope for weak enforcement, but getting arrested on the way to the campground puts a damper on the trip, for me.
