Actually you might consider doing what Frasier did with their
cabinets. You mount the back panel on four to six threaded studs, so
you can adjust a gap or slot between the back panel and side panels.
This allows you to tune the bass performance for the best sound.
You can install a styrofoam pyramid on the back panel to prevent a
back wave distorting the cone movement.
Doing this to the bottom panel on home audio speakers, in my opinion
offers much better performance than round ports, since you can tune
the speaker's bass performance to your listening room.