6th order box design help

[Akslowroller]

So as the title states I am starting the journey of a new system build and thinking of going 6th order. I have a couple builds on here nothing crazy. My first was just a simple ported box with two old T2 rf 15's. And my second one was a 4th order housing two HCCA 15's. And lastly was a single ported enclosure for my N2 18. All turned out great but like most of us never happy and always want more. So back on Topic I am leaning towards building a 6th order wall in a 99 Subaru impreza wagon. I bought the car just to build a system in. I currently have several if the components I need to start the build which includes my two SP4 18's and for now 1 RF 2500.1bd. And three kinetic batteries and a s**t ton of 1/0 wire. And I am sure I have more I am just forgetting. So I am hoping someone out there has more experience on this subject and can chime in on some box advice. I want to be musical and well I want to move some air. Spl is always a plus but not at the top of my list. Any advice or help would be appreciated.