Sorry, but if there is airflow, there will be dust. Unless running some hospital grade filters for the house/room, nothing will prevent dust completely. No matter if negative or positive pressure. All my systems had neg pressure, as i dont like to hear the front fans spinning and use low rpm/throttling), and have yet to see any dust coming in anywhere but the fans. but then again, i try to cover any screw/mounting holes etc, that are not being used, with tape/dampening foam.