dynamat with or without foam?

I am going to put dynamat extreme in my trunk, deck lid, rear floor board and corner panels. Someone told me to to fill the empty space and voids in the deck lid etc. with foam first. Is this a good idea or will it decrease the performance of the dynamat?

I am applying the dynamat to eliminate rattling and hope to gain a few more db`s from my subs, not to eliminate road noise if that makes a difference.

I've had great results with expanding foam sealant -  uhh "Great Stufff" or whutever - in trunk lids and rear-bumpers.

Be real careful when filling your car with it though, too much will "buckle the substrate" - warp the body of the car.  Squirt a little in, let it cure, squirt a little more - repeat.

This is a great, cheap mod to do in conjunction with a case of Dynamat.

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"I'm finished!" - Daniel Plainview

Jamie, Ham and I were talking about you last time we were in "stereo mode". What are you doing? Fill us in. Bob

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There is no such thing as free installation!