I always thought the Toughbook (or at least the ones I've seen) was a multi-panel ruggedized laptop, rather than single chunk of metal.

It's been a long time since I last saw one, I don't even know if they're still being made, but I recall the case being milled out of a chunk of magnesium alloy.

Maybe I'm wrong though, as I said it's long ago.

They're made out of magnesium and are multi-part. The trick is they make the internals somewhat waterproof (at least water passes through quickly) and suspend the entire mobo on rubber shocks.