Galvanic corrosion occurs when steel (and some other metals) comes into contact with aluminum along with moisture.
For corrosion protection, the entire frame is immersed in an e-coat solution at the factory and an electric charge is applied.
However, steel body parts obviously can rust and often does regardless of the e-coat, especially is high-salt areas.
Northern countries in Europe where salt is used on the roads during the winter, vehicles may better get undercoated.
Ford Transit vehicles come treated from the ModCenter, if customers don’t want to see rust underneath in a short while.