I am doing the same to my 20 SF adding a battery under the console. I chose the switch from Bep marine defender.com has it.
http://www.defender.com/product.jsp?...9265&id=776709
IMO the Bep cluster switch is a cleaner install check out both wiring diagrams. Good luck!!
http://bluesea.com/files/resources/i.../990310020.pdf
http://www.bepmarine.com/media/produ...73148082df.pdf