Good question! Here is a link to website that lists the various states towing laws/requirements...
But, I will add my question too! I am licensed in AZ with class D (regular license for driving a car) and that is all that is required in AZ for towing,
However, we are soon to leave on a trip that will take us through NV, which requires class A or B with an "R" (RV) endorsement. DO I need that if my rig (and myself) are licensed in AZ? I wouldnt think so....but.... looking for wisdom here.
(EDIT: Just went to the NV DMV website and now I can relax.... the Class A or B, plus the endorsment (which is now "J" instead of "R") is weight based and my rig comes no where near the weights required to have those licenses/endorsements). My recommendation is to go visit the DMV websites for the states you will be traveling in/through (or call them) to find out their local laws.