Am I missing something? What's the point of a fan inside a completely sealed metal enclosure? You would simply be moving around heat unradiated through the metal...you'd be better off with a fat heat sink.
The problem is the visual in your head is thinking normal motherboard and case.
Instead, think motherboard the size of a pack of cigarettes, fan the size of a quarter, and large metal enclosure.
Less like a bull in a shoebox, and more like a mouse in a gymnasium.