Step 1: Materials
1. Screaming Skull found here for $11
2. Bondo Body Filler
3. Bondo Glazing & Spot putty
4. Plastic Epoxy
5. Sandpaper 60/80, 220, 400, 600, 800, 2000
6. Tack cloth
7. Primer the kind you can sand
8. Spray paint of you choice. recommend Kylon Fusion because it is made for plastic.
Step 2: Mounting the Skull
After the epoxy has dried mix your bondo. Just follow the directions on the product. You should have a nice light pink color when it is mixed properly. Make sure you tape off the hold on the top and bottom of the case. It will be a pain to get the bondo out of the holes. After you have applied the bondo you can remove the tape. Make sure to remove it before it dries though.
Let the bondo dry for 30-45 minutes.
You can learn more about bondo here.
Step 3: Sanding and More Sanding
Start with the 80 grit sandpaper and smooth out the bondo. Once you have it blended nicely at the edges and it shaped the way you want it you need to apply the bondo glazing putty. Let the glazing dry for 30 to 45 minutes.
After the glazing its dry use the 220 grit sand it off. The only red left from the glazing should be in the imperfections in the bondo.
Apply another coat of glazing and sand it with the 400 grit sandpaper. Then apply a 3rd coat and sand with the 600 grit sand paper.
Step 4: Primer
Tape off the front side of the case so you don't get paint on it.
Once you have the surface completely smooth you are going to apply 3 coats of primer. Allow them to dry completely. I'd wait at least 2 hours to be sure. Using the 800 grit you need to wet sand the primer. Sand it down so that there is almost no primer left.
Then apply 2 more coats of primer. Wet sand again with the 2000 grit sand paper. You can find this at an automotive parts store or walmart.
Step 5: Painting
Now that you have it completely smooth its time to paint. Even though you have the surface super smooth the paint will still stick. If you are using Krylon Fusion paint because it is meant for plastic, which is even smoother than you have your surface now.
Paint as desired. I used 3 coats of flat black to minimize glare and show depth better.
If you are looking for a mirror finish you can read this instructable.