Help with enclosure for 2 ZCON 15's

I'm trying to design a center port enclosure and the port is confusing the hell out of me. I am assuming I am going to have bends in the port.. So would that change my # of common port walls to 3?

Also, when measuring port length, do I measure down the center of the port, or divide it in half and measure the centers of the two halves?

Any and all help is much appreciated.