Box help for B2 HN12v3

[Kris4b11]

Hey everyone, its been a while since I have posted anything. I've been out the car audio game for a while. I currently have a single B2 HN12v3 dual 2 ohm powered by a B2 Mono in a 2.8ft^3 box tuned to around 33hz. I would like to build a box that would port out the armrest (ski hole). I need some help as I have never built anything that was not either a slot or aero port box. I was able to meter it and it pulled a 139.9 sealed @ 40hz. Spl is not my goal. I am leaning more towards sql.  If someone was willing to help me design something or even point out how to calculate a external port I would greatly appreciate it. The max dimensions I have to work with is 15h x 30w x 18d ( if I could shrink depth by any I would be happy)