Buy baltic birch (0.75 inches thickness from a local wood store or home depot ) and paste two sheets together, so the thickness is 1.5". Your cabinet maker/carpeneter who buld the box can easily do this.
Then build (or get built) a box, 18 in wide, 18 in high and 12 in deep.

make a round hole in the box, near the bottom, 1.5 inches in diameter.
Leave the hole as is, but make sure it's round! No port pipes needed.

Stain the box as you like and seal the stain.

Mount the driver nearer the top of the box, but still somewhat in the middle of the box.

Put the speaker terminals at the back (parts express sells some good cheap ones).

Make sure the box is well sealed (use caulk) and put some thin carpet on all sides on the inside. Put a deflex pad or something at the back of the driver , on the inner back wall.

Put the speaker on the GROUND, facing slightly up, and listen to it sitting on a couch.

This should get you bass down to about 40 hz and take care of the off axis requirement.

Enjoy!
-akhilesh