Simply put, if you only have 1.5cu to work with, you shouldn't do it. If you came to me to want to do it, I would just because you are paying me. Not in any way shape or form saying the sub is bad itself, I just like to know I am not smothering my money until it is useless. IF you insist to keep the box the way it is, I would agree with JimJ, stuff it with PYF (do not be stingy with it if you want to hear some good "thump") and hope to God that it can sustain the little room it has left.
Precisely... alone with a keyboard in a empty garage until my first appointment is here...