I'm not sure the majority of class a motorhomes exceed that number. Large DP's yes, smaller gassers no. But to answer your question, I think here in SC the number is 26,000 lbs before you need a special license. The same license is required if the combined lengths of the motorhome and something being towed exceeds some number which escapes me at the moment.
2016 Newmar Bay Star Sport 3004