I have a follow up question (since no one jumped on my 6x9 idea )

If I put a sub under the med kit... do I need to enclose it in the trunk? Or can I let the trunk be the enclosure? What is the negative to doing it this way?

I have no idea how to build or size the enclosure... plus I don't want to lose the trunk space.

And I can't tell but it looks to me that the sub speaker will be too close to my fuel tank (diesel). I havent started cutting yet so I could be wrong...