The roof gets foamed.

Anybody who knows these dodges knows the roof is hollow and bongs like a drum. Years ago, I foamed the inside of my crewcab an it made a big difference. I rigged this copper tube to squirt the foam as far as I could into the roof. I wish I could say it worked. It blew apart. So I taped two straws together and reached in as far as I could. Then I did the rest from the dome-light hole seen in the top right of the pic.
One thing about this stuff. You find where all the holes are.

Here is a shot back up inside before it expanded completely.

While the foam was still soft, I started welding in the insert.