Joined: Nov 2016
Dynamat is a resonance damper, and you only need to cover about 1/4 of the surface to get maximum effect (unlike what most people do). It just keeps metal panels from ringing like a gong, and that's about it. To dampen sound, you need something else. Jute matting, or some kind of poly-cell stuff works great. There are tons of sound-damping materials available, and many are cheap.
The asphalt hanging 'curtain' thing on Cougars (and Mustangs too I think?) between the rear seat and trunk doesn't stay up well, or do a great job. I would not use styrofoam, for several reasons, not the least of which being that it squeaks, and it's really easy to damage (putting stuff in the trunk). I think most any kind of sheeting would work fine, especially if you put some kind of cloth on it like the material they use to wrap speaker boxes. It would damp a lot of sound, anyway, and look nice from the trunk. My plan is to cut out a steel sheet to fit, and dynamat/put cloth on it, and then mount a subwoofer in it. As an added bonus, it should help stiffen the chassis and body significantly.
I smile a lot. It makes people wonder what I'm up to...