Box Help: Nightshade 15

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So I just bought a single Nightshade 15 for the trunk of my 2007 300C. I'm just gonna figure out what works best for the box so as to not block my spare. I was considering porting a box towards the back seats, with the sub inverted on the back of the box (so you can see it when you open the trunk). Any problems doing this? Having the sub inverted would let me fit the box more tightly towards the seats in my opinion, but I'm new to box building.

Thanks for any help