Gold bar box

Recommend printing cover standing up (place on face and select the short end with a slight frame around the opening). I found this makes it a bit more durable as the layer line are encircling the box when inserting. You might need to use a brim in this case to reduce risk of print failure, though the one in the photos was printed without.

Depending on precision of your printer and how much post-processing you are planning on doing, you might want to scale the cover part by 1-2% to make fit less snug.