My first car was like that, huge holes. Just so happens that dad replaced our hot water heater right then, I took the sheet metal off the outside and used it for floorboards. He also trashed a steel swing set no longer used by my younger brother, and the skinnier tubes on that made perfect ribs under the sheet metal to support it. New carpet on top, new (much better) seats from a Euro sedan, and the inside looked and felt great.

I remember decades ago (about that time or before) asking my dad if chrome-moly steel was stainless, and he said, "Oh no, chrome-moly rusts like a b!tch." I now know that it has chrome content below 1.1%, that's well below stainless which typically has about 13% chrome. There are "semi-stainless" alloys with about 8 or 9% chrome, where rust resistance is not the goal, but the chrome is there to increase hardenability (can harden without a fast quench, such as just air cooling) and other properties, and that chrome content gives limited rust resistance, like enough for a kitchen knife that is hand-washed, but not a salt water dive knife.

There's an exceptionally good blog by a metallurgist, who wanted a better knife steel and theorized that most knife steels have too much chrome, so he did precise calculations to have just barely enough chrome to "saturate" the iron, and thus no excess to easily link up with carbon to form chromium carbides, which are hard but not real hard. As a result, the carbon would hook up with vanadium to form vanadium carbides which are very hard, in fact too hard for typical aluminum oxide sharpening stones, that required harder ones. All the other properties were great too, including toughness, the guy did the hat trick on his first attempt, helped greatly by a modern computer program "ThermoCalc", which predicted behaviors before actually making an alloy. I've learned tons from the website/blog, things I couldn't grasp easily in metallurgy classes. Site is https://knifesteelnerds.com/ . The steel he designed is MagnaCut, there's an article about it, and it's now showing up in the commercial market.