Ok, in that case I'd probably go for a total of 45 sq in of port area. I still thinks Skars recommendation is a little low.
Assuming the net volume is 3.5 cu ft total, and you want to tune to 34 Hz, a 45 sq in port is going to need to be around 23-24" long. Keep in mind the layout of the box is going to change how long the port needs to be, but that should get you close.