While California my accept your out of state DL when towing doubles, your rig still has to meet the state length regulations.
35401. (a) Except as provided in subdivisions (b), (c), and (d), a combination of vehicles coupled together, including attachments, may not exceed a total length of 65 feet.
(b) (1) A combination of vehicles coupled together, including attachments, that consists of a truck tractor, a semitrailer, and a semitrailer or trailer, may not exceed a total length of 75 feet, if the length of neither the semitrailers nor the trailer in the combination of vehicles exceeds 28 feet 6 inches.
For the 75 foot rule to apply, you need to be driving a mdt or larger. A truck with a pick up bed doesn't meet the definition of a truck tractor.
I'm basing this on over thirty years do California law enforcement experience.
California towing laws aren't very clear, easy to understand for resident. I had a DMV clerk argue with me that I didn't need and endorsement on my passenger vehicle DL to tow a fifth wheel over 10k but below 15k. I had to show her the VC section before she believed me. Very few California drivers are aware of that requirement, and the rv sales lots never seem to mention it.