We play Fitz at 13 but just use him like a prop. He is best at prop these days or in the second row, 13 is the last place I would choose to play him.

Fitzgibbon's played most of his career in the 2nd row hasn't he? Moved to 13 as a 3rd prop in recent years as he's slowed down. I've never seen him play as a 'proper' 13, and I don't personally think he can.