What the newcomers may not be aware of was back when K-F products and Willys products were new after World War II, undercoating as such or other metal protecterants (besides "bonderizing") commonly used in the 1960's and later were not prevelant in the United States. The only way you could get a Kaiser, Frazer, Henry J, or Allstate (along with a Willys product) was to have the vehicle delivered to its first retail owner at the factory. I don't know what Willys-Overland and successors charged, but K-F charged dealers $20.00 with a suggested retail of $25.00). A lot of dealers either did not have the room or the interest (or both) in creating an undercoating area so they could do the work. The result is that cars in the midwest, plains states and parts of the east coast were succeptible to exposure to salt. How things were sealed by welds determined where the worst rot would set in first. Even Nash and Hudson, leaders in the postwar unitbody field had severe rot problems, even though the bodies were literally dipped in corrosion-retardant materials that were electrostaticly bonded to the metal of the body. There is a reason why you see even fewer Nash and Hudson cars today...I walked the old junk yards and saw the deep coil springs popping out the top of the inner fender towers and even through hoods as rust weakened the metal the springs were attached to.
In the case of the Henry J and Allstate, the same 20 gauge steel sheet used to stamp body panels on the Henry J was used on the Kaisers and Frazers as well. It was lack of treatment with rust inhibitors or undercoating materials that did cars in. Most Kaiser-Frazer products were sold east of the Rocky Mountians and north of the "Mason-Dixon Line and the Missouri Compromise line" going from the Atlantic coast, west across the continental United States. They had good reason to call this part of the country "the rust belt" and you had outfits like Rusty Jones, Ziebart, Polyglycoat and other aftermarket undercoating people operating into the 1990's.