That is a great looking box but I'm afraid the air volume wouldn't be great enough to give it a real kick. As always, I'd sooner lay a custom fiberglass enclosure to replace the rear interior panel and cargo net. It's a more central location, it won't get kicked, and you can build it to hold a fairly large air volume.
I'd be more worried about the JL Audio enclosure, one reason I never bought one was that I figured I'd have to replace the mesh every other week if I wanted to keep it looking new.
This box looks like it was custom made. You could probably do something similar yourself with a bit of fabrication skill.