No need to research the permit. Both times we went for the day, we took the ferry and just walked up to one of the people renting cars. They just include the cost of the permit. Both times, the car was not what you would want to drive at home, but it served its purpose. Easy island to navigate and little traffic.
Having been to Virgin Gorda and SXM twice each in the last 3 years, there is no doubt they are very different, but we love them both.
Scott