OK, Robbi:
blah blah blahblah, blah blah. (LOL)
It turns out this Blue Seas battery selector switch has AFD (forget about what it means - you need it) built in:
http://www.bluesea.com/product.asp?Product_Id=31165
I just put one on my boat and plan to swap out my other no-doubt-soon-to-fail...