subwoofer box

I am trying to figure out how to install either 4 or 6, 6.5” scar audio subwoofers to my frontier. I want to have them front facing under my rear seats. Would someone be able to help with the dimensions for a sub box. I am getting really confused due to the curved part under the driver side rear...

Nissan Frontier 2005-2015 Crew Cab Truck Dual 10" Sealed Sub Box Enclosure for sale. I’m trying to get this thing out of my basement after recently trading in my Frontier. I posted it on eBay for $100 after finding that $113 is the next cheapest option online, but willing to negotiate on my price.