Dynamat is for sound systems, it helps keep sound within your car. It does little to reduce sound from outside your car. Save your money on those expensive mat products.
I belong to the Corvette Forum and most Vettes are using a simple product you can buy from Lowes, or Home Depot. Frost King. It has thin aluminum on both sides and does an outstanding job of sound proofing. I have it in both my Vette's. Just use spray contact cement and go for it.

Link to give you an idea of what I'm talking about. This person pre-cuts the parts for installation in a Vette. Lesson's installation time.

http://www.exoticvette.com/

'07 HCH w/Nav, '04 Corvette Z16, '98 Corvette Pace Car, '04 Chevy Avalanche.
HCHII Mods: Tinted windows, PIAA 4150K Headlights, PIAA 004X Fog Lights,T/P F/R 48/46 nitrogen.