ok well looking to build a new system for my car im planning on building a 4th order bandpass (never build one before) and well wondering if anyone can provide some info on how to go about it for this sub/amp/car set up im going to provide all info and see if you guys can help with a box design thanks alot!

2008 lexus es 350
sub: 1-12" jl audio w6v3
amp: jl audio slash.v3 600/1

really looking to port box thru rear seat fold down arm rest