The tin box I wanted to use as a case for the mini boombox had "issues" that I thought I could get around. I knew that the metal of the box, unless insulated, could short out pin connections easily. My idea to insulate the box was to coat the inside in vinyl adhesive contact paper.
That worked OK for awhile - until I started moving the pi and other components around inside the box. The sharp pins of the components pierced the contact paper and started to short out. My solution to that was to case up the raspberry pi (a box within a box) and put insulating tape around connections and other potential trouble spots.
To create a pattern for cutting speaker holes, I placed a piece of paper over the back circular cone of the speaker. I dragged a pencil over the circumference of the speaker, which left a dark line where the edge was. I cut this out, taped it to the box, drew a line around the pattern with Sharpie. Remove the pattern, and Dremel the circle out. Though rough, it's good enough - inserting the speakers through the front of the box covers the ugly hole.
I used acorn nuts for the speaker holding screws because they matched the color family and metallic style of the box. I added a metal "spoon handle" available at the hardware store, also in similar color scheme, screwed through the lid as a carry handle.
The DC in is straight 5V. I soldered it to a piece of perf board (adafruit prema proto board) and then the switch in line to a USB micro cable with the USB A end cut off. The micro end I kept and used to power the raspberry pi. The LED part of the pushbutton switch I connected to Tx on the pi. This will supply power as long as the raspberry pi is up, and drop power when the pi has safely shut down. When the light goes out, the pi is down, so it's safe to push the button to turn off power completely.
Continue to Part 8 -Controlling your Music