I made the guts out of old bike inner tubes, if you want to make your own I posted a tutorial here http://thestrangestitchery.blogspot.com/2010/10/guts-how-to.html
Oh, and I saw your costume - unbelievably amazing! The tentacles are f*ing awesome! Really wish I could make it to ComiCon to see your kick-ass Ursula in person!!!