I've looked at a few here, even ones that live near the coast and at worst there was some minor rust on versions with steel wheels and not really anywhere else.
Surprised by that. My mate had a Vito, here in Sydney and the roof rusted through around the a pillar gutter join and plenty of rust in the door jambs. He swapped for a Hyundai iload and has enjoyed that, trouble free for about 8 years. Lives by the sea so gets plenty of salt in the air.
Not sure it is the salt just poor metal and paint. Especially when the mercs become worse than transits for rusting.