Re: Was looking at this guy's site...
A lot of stuff involved in car audio is making things fit where they aren't supposed to go. I know those older GM trucks don't have much under the carpet from the factory and I think I know what you mean about the trim panels not wanting to fit anymore. Your carpet is probably not backed with jute and the factory never put in the money for real soundproofing. Some cars today have quite a bit done for sound deadening and you don't need all the products SDS sells.
My recommendation is to send an e-mail to Don and ask for his suggestions. I don't know if he's worked on your type of vehicle but he'll know what to tell you. His e-mail is linked at the bottom of the page on sounddeadenershowdown.com
New online business launching soon. Specializing in car audio system designs and sales for those seeking great sound.