I had a go at painting today also, but I thought that before I unleash my n00b skills on the case interiors, I'd try something smaller, my keyboard! I'm actually surprised at how well it turned out, although I did bodge the corner as I got distracted, and it now has runs on one corner. This will be easily rectified with some sanding paper and a respray tomorrow.
First attempt...failed! lol
But, the rest of the keyboard looks amazing. Btw, I have a tin of red metallic spray paint for automobiles and also a clear lacquer, however I didn't use the lacquer as the finish produced was almost the same to the gun-metal case I have, only red. Also, I made a make-shift paint den using a clothes airer and a sheet so no dust could fall, with a fan underneath for ventilation, I'll post picks tomorrow to show you what I mean. The best thing I can say though is take your time and do short but quick sprays evenly across the object, let it dry then repeat with more short but quick strokes in opposite direction. This gave me an incredible finish.
The paint I used is Holts Auto Spray Paint Metallic Red HDREM07 if you can get that stuff but in a color you like, then I would recommend it.
I will post pics of my keyboard once I respray and am happy with it totally!