Dynamat / Peal n Seal... yes or no

Where is the best place to but Dynamat or B-Quiet? I see it on Ebay and know you can buy direct... but does anybody have a good source or discount code for a killer deal?

DGC- your suggestion is my main concern right now- need to make sure leaks are ALL found. I think the cowl vent by the windshield as well as the seal around the wipers may be main culprit. I know the drain for the back window is rusted- but that affects just the trunk. Gonna pop a few beers tomorrow and hit her with the hose... and hopefully rectify all issues promptly.
Has anyone ever just sealed up the cowl vent by the windshield?

Good info Scuba- it was causing some concern. I was reading a study where they say on a typical 95° F day, the air temperature in a car that has been previously air conditioned can exceed 120° F in just 20 minutes! And it jumps to 149° F IN JUST 40 MINUTES! Your dashboard can heat up to more than 181° F to the touch, the steering wheel can exceed 159° F, and a car seat can reach 162° F and more.

Im not worried about thickness combining sound deadner and mass backing as each are only about 1/8" and I dont think 1/4" will make a big difference. Worse case scenario... I may have to bend the gas pedal slightly to give me a little more acceleration gratification!

Thanks to all for advice... any other input is welcome.