To the OP's question of wire size:
www.bluesea.com has a very helpful wire size calculator behind the circuit wizard radio button.
Enter 24V, 12A, 60 ft for parallel wired panels.
Enter 32V, 6A, 60 ft for serial wired panels.
Wired in parallel is great for days when the sun is plentiful. Enough voltage can be produced to easily overcome the parasitic losses and deliver the most amperage (12A max) to charge the batteries.
Wired in serial is prefered for days when the sun isn't as cooperative and the panels cannot produce the 13.6V + parasitic losses necessary to charge the batteries. This option would only charge at 6A max.
YMMV,
Cliff
