See here for a reference on the various options, most of which are drivable under a standard license. The big difference tends to be when you get into things with air brakes, which requires a special endorsement or the truly huge sizes. Most of the restrictions are based on the towing/hauling or hitch capacity of the vehicle pulling them though, as opposed to the license of the driver

https://www.rv.com/rv/rv-classes-explained/

Also, this is in Canada but my understanding is that the US is much the same