The show you’re probably thinking of is Trapper John, M.D. The doctor was Dr. George “Gonzo” Gates, and he lived in a motorhome/RV in the hospital parking lot.

A couple of other details point to the same show:

  • It was a medical drama from the late 1970s and 1980s.
  • The RV-in-the-parking-lot detail is explicitly associated with Gonzo Gates.

If you were thinking of a different doctor-in-an-RV character, that’s the strongest match from the available results.