When I worked at the frame plant, I went in the door there just as processes were changing. The frames originally were dipped in a hot wax treatment--which is what that gooey stuff on the frames of lots of Ford vehicles was. For the 2002 Explorers, the frames [which we started running in January of 2001] were made from, essentially, formed heavy-gauge [up to 1/8"] sheet metal that was MIG welded from a collection of components. They were built as a front mod ["module"] and a rear mod, and those were joined at a Y in the assembly line referred to as "marriage and makeup." Once the frames were completed, they were stacked via special spacers, and stacks of 8 or 10 frames were put through an electrostatic coating process. There were several dips used; one removed the light oil coating from the frame components, another "rinsed" the frames, and then they went into the E-coat immersion bath.
http://www.clearclad.com/clearclad_resources/ecoat.htmA German company named Eisenmann [with an American branch] set up the E-coat operation. But with the total immersion system, all of the nooks and crannies of the frames were completely coated. [The trailer hitches, which was my specialty area for a couple of years, were powdercoated on the outside; but the inside got E-coated when the rest of the frame was immersed. The powdercoat was slick enough that the flat-black E-coat didn't adhere to the outside of the hitches.]
NOW...if you could find a place with an E-coat tank large enough to immerse the cab--I think your rust worries would be gone, at least for this lifetime. And NO, I don't have any idea what E-coating an entire cab might cost.
My posts contain my own opinions...your mileage may vary, void where prohibited, objects in the mirror may be closer than they appear, and alcohol may intensify any side effects.