I'm a new owner of double cab tacoma. I recently was wondering the same thing. I removed the glove compartment which is real easy by the way and I found a little door right above the blower motor, length and size of a standard cabin filter. It looks as if the a filter would slide right in. I see no other purpose of why that door is there. Maybe the filter has to be bought as an accessory. I'm gonna call the dealership tommorow and find out .
