Porting a downfiring box need some help

[plyhammer 10+ year member]

I am going to put 2 12" brahmas in a downfiring box under the rear seat of my ram quad cab. Each sub will be getting 500 rms at 2 Ohm. I want to go with a vented box because I would like to play around at the local spl comps. I can get roughly 4.4 cubes out of the box (raised the rear seat) but the box is not a square or rectangle like most all the vented boxes I see. Mine would be 54" long and 18" deep (from front of rear seat to back of rear seat). the problem is that the rear of the box would be only 9" high and the front would be 11" high. So the vent would start out at 11" and get progressively smaller as it went toward the back of the box and then when it makes the L turn at the back would be only 9". Will this work? It is recommended to be tuned to 28 hz. If it is possible how long do I have to make the ports? One port on each end of the box? Do I need a divider? thanks a ton. P

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