Rust will kill a car. I've had to junk a car due to rust alone, had it not rusted out structurally to the point where the control arm moved laterally, because there was no socket left in the subframe to hold it, I would have kept the car.
Auto manufacturers literally tell you to wash the undercarriage if driven in salty conditions inside the owner's manual. They tell you that because they know undercarriages and structural components exposed to salt will rust. It then surmises that you can either let the salt get on and wash it off like the manufacturer says or use fluid film or krown and wash that off instead at the end of the season. Doing neither would be stupid and against manufacturer recommendation.
Auto manufacturers literally tell you to wash the undercarriage if driven in salty conditions inside the owner's manual. They tell you that because they know undercarriages and structural components exposed to salt will rust. It then surmises that you can either let the salt get on and wash it off like the manufacturer says or use fluid film or krown and wash that off instead at the end of the season. Doing neither would be stupid and against manufacturer recommendation.