[naraht]

Found at least three other references to steamspunk as steampunk related porn.
as well as...
Castle:"What's to know? His family is powerful, his spark burns strong, he's already taken with you,"
Castle: "—and you cannot deny that he has a magnificent death ray. "
Agatha""That's hardly a basis for a stable relationship."
Castle: "All the Wulfenbach Sparks are known for their oversized machinery, you know. I mean, just look' at Castle Wulfenbach. What exactly are we trying to say, here?"

and
Castle:"The master bedroom only sleeps six"