Ziebart had a system of spraying the undercoating on a car but they drilled holed in places and left crappy looking plugs behind. I've noticed that body rust thru isn't nearly as common as in the past. The only vehicle I see now is the rusted out wheel wells is cars that actually live on the coast, shrimpers are the worst.
My 2019 F250 had quite a bit of unpainted cast assemblies under it. its just developed a light skin of rust on it.
