I would have bought a clear ATX case and I did have a look to see what was avalible, but the only clear case's I can find are tower cases. Even if I was to lay a tower case on its side it would still take up a good amount of space. The case I built is 370mm X 240mm X 160mm as apposed to a clear tower case (470mm X 195mm X 440mm). Since I've installed my new case I've managed to free up most of the boot space I'd lost when I had my old car computer.
I'm going to try to get some more pictures of the setup using a better camera in the day time, so I can show the entire installation (relay connection to alternator etc).