There's a Q & A (and other goodies) over at the official Finn site. It opens:
Question: What inspired you to write Finn?Read more from the Q & A.
Jon Clinch: Ever since I first read The Adventures of Huckleberry Finn, I’ve been haunted by the image of that dead man in that floating house. It was just too creepy. And upon rereading the book more recently it seemed to me that the scene’s place in the novel (just where Huck and Jim’s story starts taking off) conspires with its anonymity (the corpse isn’t identified as Finn’s until the end of the book) to keep readers from giving it too much attention. No doubt plenty of people slide right past the details: the markings on the walls and the calico dresses, the black cloth masks and the child's speckled straw hat, the baby bottle and the wooden leg. There was an adventure getting started, after all, and this mysterious scene—populated as it was only by an unidentified corpse—was just one more picaresque detail.
I wondered how Finn had come to die surrounded by those mysterious artifacts. The conventional wisdom, that the floating house was a brothel, didn't satisfy. I preferred to believe that Mark Twain had left in that crowded room a set of clues—not just to Finn's death but to his otherwise unknowable life. In Finn, I set out to follow those clues wherever they led. And they set a course down some dark and unexpected waters.
--Marshal Zeringue