The powder-coated part will not rust.

But if there's a tiny bit of steel not covered by the coating
and it gets exposed to moisture (in your case, rain), then
it'll rust, spread and creep underneath the coating.

In time to come, you'll find yourself having a "marvellously
beautiful" powder-coated door with patches of rust.

Bottom line: Get a good contractor with quality workmanship.

Hopes this helps!