Appreciate your follow on comments bartamos. In your travels have you heard of condensation being the primary culprit attacking the front inner and brow structures in these TF cabs. Just not sold on the fact these hidden areas could potentially have created its own atmosphere...these trucks weren't built that tight. You mentioned leaking drip rail, holes in outer roof skin, I don't immediately show signs of that going on here. The other quite probable issue was the poor metal prep treatments if any at all in 1959. I be willing to wager that voided area was just ignored and sent down the line. Shoot they weren't suppose to last 50 years...right.
The largest issue is as you suggest, the vehicles were assembled and then sprayed. The area behind that front panel is bare metal.. Look at the following picture after said panel has been removed, note the lines showing exactly where the condensation ran down inside, and the larger circles at the top of the panel where the condensation droplets collected..
https://www.hotrodders.com/gallery/data/3651/IMG_2172.JPGHere's the complete thread on how Roger fixed the area..
http://www.67-72chevytrucks.com/vboard/showthread.php?t=582950Condensation most certainly was an issue in these vehicles. They sat outside in the sunlight with windows rolled up, and the heat inside also generated humidity. Cold air at night and the humidity cooling against a now cold sheet metal roof and yes, drops of water starts to form just exactly how it also happens inside a metal building. The water would then run down to the lowest point it could reach. Any dirt or debris that may have settled in those areas now becomes a moisture trap as it absorbs/collects moisture.... well on it's way to forming rust..
