I would of done like 4 or 5 layers before filling it in with foam. Well not 4 or 5 but I would of done a good amount. I feel like if thats where you face the subs towards than thats where your biggest lost will be in pressure so you should over kill it there if possible. Yea ford bass has no idea what hes talking about. 02zetech is right making the corners round means less turbulance in the air.
I listened to 2 dc level 4 8s in a box that was no bigger than 4 12 packs put all next to each other with an aero port( all inside the box) tuned at 50hz the dude hit 144 all the way from 55-30hz.
he was only giving each of them 1500 watts.
He actually let me stick my hand in through the port to feel his box. The entire inside was circle and I mean the entire inside... It was all one solid piece of kerfed wood. he then went on the outside of it and put 4 pannels around it to make it appear square on the outside. but there was not a single 90 degree angle in the box and it was way to small for the requirments of the sub. it being that circular is what allowed him to get such a high number and flat response.
He also had 6 runs of power and 6 runs of ground. Going to an oldschool crunch ground pound 3000.1