spare tire sub enclosure

Car: Saturn Aura Equipment:Alpine Type R 12" 3rd Generation,Alpine MRPM500 I'm going to be making an enclosure that fits inside my spare tire. The spare tire is on a 16inch wheel. I was planning on using a 16inch sonotube thats 9in long. This should give me enough air space for a sealed enclosure. I would also use poly fill. My question is once I put the spare tire over the enclosure and put the trunk floor over that how will it sound ? Is it a good a idea to make a new floor peice that has a grill in the location of the sub?

I'm having a hard time even picturing how this is even gonna work. Your most likely gonna get a lot of unwanted rattling noises for one.**advanced mecp certified

I would like to build something similar to this. I've built quite a few fiberglass enclosures in the past. I never thought of fireing the sub down vs up. How does this affect how the sub sounds.

http://www.abt.com/product/43398/JL-Audio-94089.html?utm_source=scfroogle&utm_medium=sc&utm_campaign=froogle

So you want your sub under your spare tire? I'm thinking there is not enough room in your car to do so without making a new trunk floor, are your going to do that as well? The one you linked to is made out of a very tough material, your going to have to over engineer this enclosure to have is take the added abuse of having your spare mounted on top of it.