exhaust and underbody
 

Could insulating the exhaust of a car allow you to use full coroplast without temperature issues as the underbody of a car?

I know not to insulate the cat, but what about the exhaust manifold, exhaust pipe, and muffler?

I've read some "reports" that keeping the exhaust hotter helps reduce backpressure by increasing gas velocity.

Trying to figure out the best way to do things.