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I'm using what's sold as a/c & heat duct insulation at Home Depot. The brand is Frost King with 24" x 15' rolls for $15-17 per roll. I prepped with wire wheel, scraper and a couple coats of POR15. Once that was dry, sprayed down both items with 3M adhesive and layed it in. Keep clear of the edges and bottom of the door. Cheap? Yes. Better than nothing? I think so but I'm winging this deal as I go.
I used Dynamat because I didn't want to do it twice. I've tried cheap knocks off before and was very disappointed. Anyway, I used 2 12x12 sheets on the inside of the outer door shell, three on the over head roof panel, one on the firewall lower edge, one and a half in the footwell, one on the removable trans tunnel cover and 3 under the seat. I also put reflective heat insulation completely covering the roof panels. Made an enormous difference! Almost as quiet as my Tacoma.
I'll jump in here. I used this product throughout the interior of the cab that I found on Amazon. Inner doors, cab rear, floor, firewall and roof. Pleased with it and has not peeled away or smell. If applied right with a roller, it ain't coming off by itself.
Noico 80 mil 36 sqft car Sound deadening mat, Butyl Automotive Sound Deadener, Audio Noise Insulation and dampening.
I do car audio systems and use the Noico as well. It is a great product and comparable to the Dynamat. Doors can be tricky, but there are affordable ways to do them. The attached Youtube video was put together by a reputable guy in the audio world and is geared toward sound competitors, but definitely could be used in the hot rod/classic car and truck world as well. I will be doing this to my truck.
I did/am in the process of doing what 66V8Baby did. Dynamat inside the doors, on the roof, firewall and floorpan. It helps a lot to take the ring/echo out of the panels and you get that nice solid door sound.