Federal law clearly states any rv is exempt from having a cdl. The recreational vehicle lobbyist have made this happen as they know most retirees that have the money to buy a 1/4 million dollar coach won't if they have to go through the hassle of getting a cdl and all that goes along with it. You can jump behind the wheel of a full size semi, and latch onto your 30K lb fifth wheel with double dually axles, and so long as you're not over length, theres nothing they can do about it.
Except here in Cali. Anything over 40' (65' max) is non commercial class A/B. Even a law that states if towing more than one vehicle on a trailer, length does not matter.., you must have a non commercial. Non commercial there is no class time or haz mat like commercial, I just had to do a written for the permit, then a behind the wheel with DMV agent. Although 99.9% of people towing over 40' don't follow the state laws.