header wrap on stock exhaust manifolds?

C130 Chief said
Make sure your gaskets seal completely

When working on a slant-6, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Header wrap is a major pain in the a$$ and should be avoided on any rig you ever plan to drive in the rain.

Interesting. Please elaborate; what happens when it gets wet?