At the very least, while you have it open, put some sound deadening material on the inside. May not help a ton with insulation, but will help with the noise. I plan to use some when I have my roof apart.
When I first read your title, I immediately thought about expanding foam being used to "fix" rust
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Christian Carpenter
1963 C10 -
Frankentruck 283, 3 speed with overdrive
Overdrive wiring here
1963-ish truck bed trailer -
Half-Wit
1981 C10 -
Penny 305, th350
1995 Dodge Dakota Sport
"I'll put it simple: if you're going hard enough left, you'll find yourself turning right." - Doc Hudson