Like any steel-bodied car, the Datsun 1200 is prone to rust. Unlike the Datsun 1000, the body panels are not galvanized but only painted on the inside. Eventually rust will attack your car, sometimes from the inside out. This means that keeping the car's paint waxed -- though it will help -- will not prevent rust.
Rust treatment is not specific to the Datsun 1200, you treat it the same way as any other car. So look for rust treatment guides here: [url=http://www.google.com/search?hl=en&lr=&q=car+%22rust+treatment%22]Rust Treatment Internet Search[/url].