Dynamat / Peal n Seal... yes or no

For under the headliner, use something light. I like the foil/bubble wrap insulation from Home Depot. I install it with spray adhesive. If it does fall, it won't bring down the headliner.

I used dynamat before. The only thing I didn't like is, the carpet slides around like snot on a glass doorknob on the foil backing. Expensive, heavy, but it works.