If I understand correctly, your case is a part composed of several bodies. I think you should use the welded construction for this part and manage its components with the descriptions of the properties of the welded parts list. Then in your assembly drawing, use the detailed bill of materials to see the "sub-components" of this box.
An example; a bolt that is a welded piece of construction. In the nomenclature, this part is a detailed compound bolt with two washers, a screw and a nut.