You should not need anything else.
The idea behind dynamat type products is to prevent the sheet metal from vibrating.
If you want to save some $$$, go to the local building supply store and ask for Icegard or Resisto membrane. (the resisto membrane is available with an aluminium foil on one side and self adhesive on the other).
It is available in 39 inch wide Rolls X 33 feet long (107.6 square feet) for around $60 plus taxes.
Those product are alot less money then Dynamat and my experience when I did my 2000 Odyssey EX with the resisto brand, it improved the sounds from the speakers and reduced road noise.
Originally Posted by [iG]