If you are driving for non-commercial you do not need a special drivers license in the US. But if you are driving a motorhome with air breaks commercially you will need a CDL with the Air Breaks...
You use "an" before words that begin with a vowel sound. If you pronounce "RV" as the names of the letters, it sounds like "arvee", which begins with a vowel sound, so you would say "an RV". If you...