the bottom ported speaker is ported and has some insulation-like padding/foam for dampenning I assume. The top was open, but I closed it w/ birch ply...
You are tempting me to go to the car audio store and by some of that sticky foam type stuff that's about an 1/8th of an inch thick with aluminum foil on one side and sticky as hell on the other. However, I don't know what would happen to the tone of a cab that uses that.
I've used it in my car to enhance the bass and subdue the rattle, and it works! However, I have no idea what the tonal changes would be in a cab.