The Opel Nationals is considered the "event to go to if you can only attend one major event that year".
Individuals or groups manage regional events held annually throughout the country. Attending the one in your region is a great way to held these expand and grow. The Nationals are rotated through these regional events. The schedule is somewhat flexible and is usually set 2 to 3 years in advance to help with planning.
Post your thoughts and comments about future National's locations here.