I don't want to buy dynamat. It's probably because I'm cheap. It's also probably because I usually suck at sticking large items without wrinkles. I would like to fill the rear panels of my 2dr with standard pink fiberglass insulation. Is this a good idea? Has anybody done this before? Should I try to envelop the insulation in plastic so that it doesn't absorb any moisture?

First post on this page claims to have put this insulation inside the door panel with plastic sheathing. How was this done? Personally, I would tape the sheating on the door on the interior side of the window (not actually stuck to the window) and then put the fiberglass on the interior side of that, sandwiched between the plastic and the panel (so we're going sheet metal exterior > window > plastic > fiberglass > panel > interior). Does this sound like a good idea?

Any other good ideas for sound deadening using less expensive, multi-purpose materials?

 

Fiberglass insulation is a bad idea. This type of stuff is not really designed for sound deadening. Now unless it's really cold inside your car....step up and get some real sound deadening. Cascade Audio Engineering makes some of the best, and it's less money than the dyno wondermat. There is no real substitute for the rite stuff.