ill bite on this, even though i wasnt asked. im also copying and pastiong from a post i did on moparts, as i REALLY dont feel like re-typing it all. it took me long enough the first time.
having done this kind of thing to a bunch of cars, ill give a few tips.
1. don't buy name brand dynamat. its ridiculously overpriced for what it is. i use
http://www.mcmaster.com/#catalog/117/3497/=fqjmp1 the plastic 10% sheets. works very well. use a heat gun and J roller to work it in tight to the sheet metal. prep the surface, even if freshly painted, with a pre-painting prep. you want it as clean as if you were about to lay down a top coat of 100 a gallon paint.
2. you only need to do about 80% of the interior. the last 20% really doesn't get you any noticeable results. i use the thump method. if i hear a tinny sound, a vibration, an oil canning, etc,. anything other than a dull thud, it needs it. if,m like on the roof of my truck, theres a gap between a brace or other piece of sheet metal and the panel, work the sheet onto the gap. wit will eliminate the rattle.
3. use the stuff to cover over holes in inner structure. after you get the outer surface of the door done, do the inner structure in its entirety. you'd be SHOCKED at the sound reduction. same in the rear quarter and sail panel openings.
4. do the stuff under other bolt on parts. even when things are fastened sown tight, they still vibrate and rattle going down the road due to chassis flex.
5. cover it over with something like what has already been discussed. i prefer to put the foil side down, and glue it. adding mass to the large stamped panels in our cars really helps. do this in all the areas you can. especially the roof, firewall, floor, and trunk divider.
6. i also tend to use a third layer of insulation. i use the foil bubble wrap they sell at Lowe's as a final layer over everything. did this in my half ton, and it created amazing results with the heat and AC functioning.
i have only ever had one issue with doing this kind of stuff, and thats on a 79 corvette that i just finished. the carpets for those cars is notorious for being ill fitting (due to the production tolerances on the cars, and the various mid year changes, etc). still easily workable. just a little less defined and form fitting than i prefer. but i honestly think that was the carpets fault. on that car, due to the carpets, i only did the "dynamat" and the bubble wrap. not enough room for anything else.
a good way to estimate how much material you need is to take a tape measure and measure the various big areas of the car, rounding UP to the nearest foot. so say that you have a trunk 54X61 inches. thats 20 square feet rounded up. (5ftX6ft) reason you round up is to account for contours, mis cuts, etc. you'll wind up with some left over, but its a lot better than running out.
lastly, look at your carpet choice. stockinteriors.com has what they call the mass backing option. this is similar to what GM started doing in the 80's on their carpets. its about 1/8 inch of rubber bonded to the backs of the carpets. amazing sound reduction there as well.
hope i gave you some solutions. not all that expensive when you add it up, but labor intensive. worth every minute, though. my duster has 400HP at the wheels, with 3 inch exhaust. its as quiet as my wifes stock 2002 Subaru legacy GT wagon on the inside at 65. except for the wind noise from my windows. (still working on that solution)
Michael
