As long as the RV you're driving doesn't have air brakes then you don't need a CDL or special license to drive the RV.
I've driven larger RV's without air brakes with my regular license and have been pulled over and nothing was said about it.
So as long as the RV has no air brakes you can legally drive the RV with your regular drivers license but if you want to drive an RV with air brakes you need to get training in air brakes and get your CDL or other special license to drive the RV with air brakes.
But for regular RVs that use regular hydraulic brakes you don't need to have any special licenses.