Ive got a 2009 Ford Fusion SEL where the back seats fold down. My box is sub up, aero port to the rear. The box is not large enough to go side to side and not slide, so ill have a bit of room on each side (unsure how much just yet). I would like to take some MDF to put behind the back seats that would fill the whole made when the seats are folded down. Id like to use it for mounting my amp and such. Now should i add some holes around it for the trunk to breath into the cabin when i have the seats down, or seal it completely up? Id say about 25-35% of my driving i could put the seats down if i chose to, but they are mostly up and closed. I put 1 layer of deadener in the trunk just for limiting the rattling, but i am unsure about sealing off the trunk completely as the rear-deck would still be open for pressure to move into the cabin?