Stopped at the lumber yard for some MDF.
I've completed plans for a new subwoofer enclosure and I intend to test the design with some small speakers before I build it for pro-audio drivers.
Imagine a fourth order cabinet with an internal isobaric chamber, using two drivers of course. The port will actually be an expanding chamber of its own, horn-like, hyperbolic, to spread out the peak response curve. This is a proven design, but I have never tried it with an isobaric chamber, which will further smooth out the response and allow the drivers to take more power.