Box Design

I need help designing a box. I have a single 12" Rockford Fosgate P2 DVC 4 ohm sub, and a Rockford Fosgate Prime R500 mono amp. I have a 2013 Ford Fusion and I have about 16" height and 17" depth to work with and the width can move to get the appropriate cubic feet for the sub. I am looking to build a ported box, and I like the look of a rectangle slot rather than the round aero ports. Is there any difference between the two types of ports with SPL and SQ?

https://www.crutchfield.com/S-LCyBfxwWjoa/p_5751P2D412/Rockford-Fosgate-P2D4-12.html

https://www.crutchfield.com/S-cEe0lhjCiCs/p_575R5001/Rockford-Fosgate-Prime-R500-1.html

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