tricky box for me...help

[revots 10+ year member]

i don't know how to put this pic from paint in here so let me try to explain. my friend has an 06 scion and got 2 alphasonik 800 series 12's. here's the link..http://www.alphasonik.com/images/tech/800%20Series%20Parameters.pdf

He wants the back of the box to be 18" tall and have a vent horizontal accross the top so it blows over the headrest. Then he wants it flat for about 12-14" and then to slant down were the woofers will be mounted so he can close his trunk. he wants it between 5-8 cu ft and tuned between 35-45 htz. sorry if this is confusing but i appreciate the help.please give me dimensions.

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