I have used QuietCar a lot and love it works better then Dynamat as Dynamat is heavy.
QuietCar is a viscoelastic sound-deadening compound formulated especially for vehicle applications. It is extremely easy to use. You can apply QuietCar on your car, SUV, truck, van, RV or boat using a brush, roller or spray gun. QuietCar can deaden steel, aluminum and composite materials. Applied properly, QuietCar can reduce the noise in your vehicle by up to 80%. It cleans up easily with plain water and is environmentally friendly.
Comparing QuietCar to Mats
http://www.quietcoat.com/html/compare_to_dynamat.html
http://www.quietcoat.com/html/
I am hoping this summer I can strip my truck and spray it all