There no reason incoming and outgoing air have to have the same pathways. Fans that suck out inside air will not bring in outside air. This is pretty basic stuf

There no reason incoming and outgoing air have to have the same pathways. Fans that suck out inside air will not bring in outside air. This is pretty basic stuff. Your inlets can have absolutely no filters on them and the fans sucking out the air will maintain a pressure differential that makes sure the inlets will mostly only let air in.