My first MOD was a bed mat that I bought on sale for a jeep gladiator since there wasn't any aftermarket ones for the Maverick out yet. It was a little big and I had to cut it with a razor, works well enough :)
You can also leave the power on but turn off the button between the circulator and the defroster (the one with an arrow pointing at the person's head) and no air will flow through the vents.