4th order bandpass for type r

I've been searching everywhere but I can't seem to find any experiences of people putting alpine type r's in a 4th order. I've heard they preform better in a ported box, which I have built several but now I wanna play around with them (2 - 12's) in a 4th order.

All the calculators give me silly box volumes ex. smaller ported chamber then the sealed section???

Do any of you guys have any ideas or something you've tried that may work?

I have about 8cu.ft. to work with

Thanks

does anyone have any ideas?

These are the woofer paramiters:

epb - 63

Thanks