[Rick_crew]

Ugh. That's really nasty.

I suspect the fully-boxed frame retains crud in places that're gonna rot eventually. Probably would no matter the factory corrosion-protection treatment applied.

On these little trucks though, I doubt GM went all out to apply the best/latest state-of-the-art (for 2004) to the frame anti-corrosion treatment.
I'm sure they didn't bother to electrocoat it.
Probably just hit it with no-primer cheapo paint.

 

[Rick_crew]

My '05 was in the northeast and upper midwest most of the 13 winters I drove it. The frame looked near pristine when I sold it about 18 months ago. There was light surface-rust over the entire chassis and undercarriage, but the otherwise the frame looked fine.