42RH / A-500 in a Duster with pictures.

How a material handles load is not all about its thickness. How the material is shaped transfers the load/stress to its other facets. Those 3 and 4 sided elements in the car now are a good example. Their wall thickness is more relative to the attaching hardware used. The majority of it is 11 gauge which is very close to 1/8 wall thickness.
We cant all be engineers but we can study is/was engineered and take our cues from those examples. Hope this helps