I think you're probably going to have a challenge fitting the drivers and the vents into a box with those required chamber sizes ...
Chamber 1 = 13" x 26" x 7".
Chamber 2 = 13" x 26" x 7".
Chamber 3 = 13" x (width & depth depends on the external folding of Port 2).
Port 1 = 13" x 7" x 0.75".
Port 2 = 13" x 3.5" x 52".
Port 3 = 13" x 14" x 0.75".
In your BP8P, I see you used external ports for Chambers' 1 and 2.
In my BP8S, I need make sure Port 2 feeds into Chamber 1 and Port 1 feeds into Chamber 3.