So I have been working my way up from the floor to under the dash replacing the rusted out bits. I just realized after cutting out a bit on the overhead why it gets so rusty under there and by the air vents. Turns out the water ad pine needles etc that get in the grate by the windshield that the wipers poke through just runs down the inside of the cab and out through the air vent box! What a dumb idea on Chevys part. There is no way thats not gonna rust through, especially up here in rain country...

Guess nobodies perfect...

Done venting.