FG Enclosure Dampening

I have basically fifshed a pair of FG enclosures that fit into my rear wheel wells, I am wondering if any of you use something inside as a dampening agent. without it I think my box may sound a little too tinny. I could try getting it all done and playing around with it, but I thought I might as well find out if anyone else has done this

I was thinking of using either regular household insulation or the left over fleece that Iam covering the box with.

your thoughts???

Maybe 3M undercoating in the spray can, I read that a guy used it on the inside of his doors????

Also, is there a happy medium for dampening, or in other words, How much will I lose from my subs if I do this???

I have done more research since I posted this and I have found that there is Polyfill stuff that people are using, I believe it is called Acoustic foam & Acousta stuff, They say to line the sides top and bottom with acoustic foam and line te back with acousta stuff.

I might try this if I can find the product, but at the same time I want to keep the cost down

heres the link to the page that gave me this info, I  know it's not car audio, but it should still apply

http://www.partsexpress.com/projectshowcase/daytoniii/dayton_iii.html