I have 4 Soundstream 15 inch T4's they require 4 cubic ft for each sub net and gross is 4.25 .That's for high output tuned to 39 hertz. How far should the vent go inside the box?Should the vent go straight back or straight back then add a board giving me the L shaped vent?I need box dimensions port dimensions in full detail.I'm putting this in a 93 chevy Silverado.If that don't work i could go with a 3.5 box net 3.87 gross tuned to 32 hertz.If that's not enough info google it please appreciate it.It can be a design for 2 subs i'll just build 2 boxes or 4 subs and i'll build one box.