Need help with new box design

[coh33dkill3r]

I have 2 sundown audio x-18 d2 with a rf 2500-1bdcp I'm very limited on space but my max dimensions are 38W x 41H x 17D. Wanted to be tuned around 29-31 hertz... Thinking I'm going to have to use aero ports to save on space but don't know the first thing about ported boxes. Can someone help me with how many ports, size and length I'd need.

[Joe X]

4 6" ports FLARED would be minimum. Box would need to be bigger. But also 41H? is this a wall or what.

[coh33dkill3r]

Yes it's going in my nissan cube but have to keep my rear seats for my kids.. what would the length of the ports need to be??