CA allows double tow as long as the first trailer is a FW and total length under 65' and operator has class A with double endorsment. Brakes on any trailer over 3500 lbs. I think.
I was at the gas station and I approached a gentlman with a Class A pulling a trailer with a jeep on it and a trailer attached to the jeep that was loaded with a boat. He had CA plates and I asked him he got his setup permitted and he stated that it was completely illegal but if he was to get pulled over he would just pull the jeep off the first trailer and let his wife drive it pulling the boat.