As long as the salt is washed out of the underside, you are not parked on grass, and don't live somewhere super humid, the rust will slow down to almost no advancement.
A spray down on the underside every 5 years with Oshpo will also make it last nearly forever.
Buses are like 3 ton and bigger trucks. You can just keep changing parts, they last forever.
I will be living in mine for 20 to 40 years. That's why I stripped mine down to the skeleton. I made sure there were no hidden cavity's of rust to bite me in the bum in 10 years.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization