The Black round slotted vent in the pic is for fresh air to come in so the blue inlet tube takes that air in to the box the the fumes are sent out under the blue box and the hot air comes out the vent in the middle of the two speakers
my Propex was under that buddy seat, on the bottom mounted longitudinally. I made a replacement side panel so I didn't have to cut the original westy panel. This was all then boxed in so I still had safe and useable storage above the propex. I sold mine to Malc but will be getting one of the group buy ones