Ports length and how many

I’m looking at a wall build. For 2 nsv4 18” dual 1 subs. Max dimensions are H-43. D-19. L-57. Would like aero port design for a box.  Please help the tuning of it for ports and length. 28-40 hz is my range. 

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do your calculations on paper like us old bassheads did back in the day

If I were to know how I would gladly do that. U willing to teach ?