I think just let people be in whatever team they want, it would make seriously good racing if you had say 5 really strong teams, and 5 good mixed teams - you don't have to be concerned with winning the overall meeting but just gauging yourselves against other teams on similar levels etc.
Think how much better you'll be able to drive too after racing the same track on and off for 6 hours - it will only do wonders for your driving
