Hmmm… I thought the Porsche club events were for BMW/Porsche club members only and guests by invitation only. When did they open them up to the public?
From the website link you just provided:
Who Can Participate?
PCA Polar Region autocrosses are open to PCA members and prospective members (current Porsche owners). From time-to-time, and at the discretion of Polar Region, we host other car clubs — having our clocks cleaned occasionally keeps us humble. Due to the financial sponsorship our autocross series has received from the BWM Driving School, BMW club members enjoy a standing invitation to join us. If you belong to a car club we have not yet had the pleasure of hosting, our autocross director Chris Horne would like to hear from you.
PCA Polar Region autocrosses are not open to the general public. PCA Polar Region autocrosses are not public spectator events.