Generally, if the RV is 45 ft. long or less, and you aren’t towing something over 10,000 lbs., then you usually don’t need a special license. (This requirement vary by state).
That being said, if you’re looking to rent a luxury 45-foot mansion-on-wheels, it would be best to discuss with the owner to make sure you’re both comfortable with your ability to drive the RV. Sometimes, these type of vehicles may require a commercial license or commercial driving experience.
For more information on commercial licenses, read this.