Here is my idea, Munny. Plain and simple you want to make a case why not make some art at the same time.
This guy comes blank and is 18in tall, that should provide some adequate room to play around.
This one is a dunny but you can see the possibilities for the outside. Plus the extra room in the ears might be nice.
Here is a 20in dunny these would all make amazing cases and make anyone jealous. If you still need more inspiration just hit up the kid robot site they have tons of stuff. Also I don't think that they make these big enough but if you could work this in the car would make it a ton easier to fit more parts without jeopardizing the overall look plus your case would be something to display as functional art.