To appropriatly reduce internal energy you would want to use Owens Corning 705 or #8 mineral board (at least 2" thick for both).
You can check
here to see if there are any local - if not look for industrially supply places that specialize in heating/cooling and call them and ask. Also, I believe Readyacoustics sells the material and it is possible to find on eBay, but is far more expensive.
Since your sub is ported I would recommend wrapping the material with cloth to prevent any degraded pieces from flying out of the cab.
As far as performance goes this looks like it will help some as the material in the pictures looks like crap, but don't expect huge gains.
