I will soon be starting my trunk IB install utilzing 2 JL 13W7 subwoofers. I will be using an Industrial grade expanding foam to seal every crevice of the trunk. I will also be sealing the 6X9 holes with MDF. I plan on layering the top of my rear deck with some Magic matt 400 sound damping material, the material needs to be heated when applied and it will cure to the consistency of concrete, this should help strengthen the rear deck without bulky peices of MDF. The rear deck is comprised of 18 gauge steel, which does not do a good job at absorbing sound pressure exerted on it. I will then install my 2 JL subwoofers into the trunk on a 1" thick MDF baffleboard and will sealthe board to the rest of the frame of the car.

I will post pics of my progress, before and after.