The triangular cargo pods of the Railen are indeed actually fixed to the ship and not the cargo containers themselves. They open to fit the standardized cargo items inside. The Cargo pods are loaded like all other cargo ships, by maneuvering the cargo into them by hand, tractor beam, or by hiring NPCs to load for you. Fret not, the shield system covers the pod area. The Cargo pods will be super helpful for various uses, much like you sometimes have extra space on the sides or below your car's trunk. For example, you could attach mining cargo pods for all I can say at the moment, and note that Tractor Beams will help you with the loading & unloading as well.