I imagine that Bobby could be very difficult to write because I don't feel that we've really seen much of him beneath the surface. Sure, we've seen some background stuff but I've never really felt like I've been able to truly dip into his perspective and his thoughts (unless, as you said, in relation to Dean). Though, he's not one of my favorite characters, so that might have something to do with it. Hmm. Good luck with it, it sounds interesting.