As previous said, you divide the object into parts and build the relationship between them. A reasonable time consuming effort. So first one must ask whether its worth it. If you going to create say 5 to 10, I would say not...20 to 100 yes.
Then decide what avenue to take in regards to its use, technically or aesthetically
A method that I currently employ is to create a DC that I can change back to a solid. The DC in the file attached is of one side of the box. Right click it and save it to a designated folder as a component. Now you can change its options to size required, Then by using outliner and expanding the contents you can see two points, one where the hole / slot can be exploded twice, then another where it can be outer-shelled and exploded. These operations can be done by right clicking (context menu) and selecting the appropriate action within Out-Liner. This creates a solid side with just the front wrapper. If you require to change it then swap it for the saved component (it will update to current option selections as it still retains the cover component)
Capture.JPG
The benefits of such approach is that one achieves smaller file sizes, protects ones intellectual rights and "Dave can take it off in Cut List"
The side lugs were done using the normal make a part and build relationship
the top and bottom done using a copy method
When I built the slot or hole, I selected a rectangle on the body surface then applied a cut face when making it a component. Next enter the component, push-pull to create sides then delete the front & back surfaces. Exit then created a matching rectangle component with a cutting plane at rear, deleted the surface then moved it into position. Thus creating a movable hole components, these named "front and "back" are the first to be exploded to make a solid body with a hole in when changing the DC to a standard component.
It took me 3 hours to create this side, so probably a full days work to make a the box...you need always to consider if a DC is worth it (plus half an hour to write and edit this)