I have 2 10's in a ported box. I ran the measurments and it came to about 3 cubic feet. Im not sure how accurate my measurements were but oh well. They sound pretty good and they can hit lows well.
You probably cant find the recommended size because Alpine doesn't recommend their Type E's in ported enclosures. I have one in a 1.25 ft^3 sealed box with a little stuffing because of the distortion.
Go ahead and try the ported though. I would love to know how it sounds.