There are many ways to go about it.  What you want is something that will
rub together or absorb vibrations.  Sand works very well for example, but is
hard to keep together.  Maybe if you make a quilt and fill it with sand.
Particle board works on this principle.  Asphalt also works.  That is what
they use on Lexi' and Infiniti's and the like.  I thought about using
roofing asphalt but was worried about off gassing.  I'm not sure what they
use in Dynamat.  What you want to avoid is something that transmits
vibration.

There are loads of books at the library and a couple of good internet sites
of practical applications.

Rob G.

http://msnhomepages.talkcity.com/PassportPl/gunter01/