I think you should try diyaudio.com (subwoofer or caraudio forum) for full help. They're probably gonna ask for the Thiel Small parameters, so be prepared. Coincidentally, with a 4th order BP, the low end is tuned by a closed chamber (without ports), the ports tune the upper part of the spectrum (around 80 - 100 Hz) and a port surface area that's 1/4 of the drivers combined Sd is a good starting point.
Best regards Cubo