I'm just quoting my source at the Grapevine Inspection from several years ago. He was the commander there.
Doubles towing was no longer allowed when I retired in 2003. Prior to that first had to be a 5th wheel and second a watercraft trailer. No exceptions.
I'm speaking of regularly licensed drivers. A CDL brings a whole different ingredient to the table.
The regular road officer is instructed to avoid commercial enforcement because it is so complicated, changes ALL the time, and requires 5 weeks of additional training. That generally includes such violations as length, # of trailers, etc., BUT they do stop and write moving violations AND may write overlength, overheight, lights inop., common horse sense violations if they are comfortable with doing so. That activity is closely scrutinized by sergeants and generally discouraged.
All that being said, not difficult to judge, stop, cite, AND direct to unhook overlength combos. There are tolerances but they are inches, not feet.
I spent 33 years with CHP and do not recall any laxing of commercial laws, rules, and regulations except when the gross weight was upped to meet federal standards for interstate trucking. Generally speaking, the same rules apply to rvs though there are some exceptions.
I would call commercial vehicle section at HQ in Sacramento to get the latest law AND KEEP IN MIND it is constantly changing.