Found an interesting CA DMV link re license classes and towing capacities for vehicles designated as housecars, begins on page 4, in their book titled "Recreational Vehicles and Trailers Handbook". You may have to cut and paste the link.
http://www.dmv.ca.gov/pubs/dl648/dl648.pdf
Class C license (CA's standard issue) and driving a housecar (rv), for max length you must be 40' and under and for max weight you must be 26k for 2 axle coach and 6k for 3 axle and can tow a single trailer up to 10k, including a tow dolley if used.
Class B non commercial license, you can drive up to 45' and tow a single trailer up to 10k.
Class A non commercial license, you can drive up to 45' and can tow over 10k for a travel trailer and over 15k for a fifth wheel.
Something intersting might be found here
http://www.hitchemup.com/statetowinglaws.htm