Add an intelligent split charge system.
Otherwise if you want to bring the auxilliary batteries up quickly from the alternator, you won't be able to, and 600w is a pretty slow charge for that amount of capacity if they run flat, and that's if the charger can actually push out that amount.

I'm at work just now using my phone to reply, but I'll post later from a proper computer with some pointers for what you're trying to achieve.