All Classified forums require a Site Supporter subscription. It is only $25 per year and you can buy and sell whatever you like on the forum. To become a Site Supporter, go to Your Profile and select "Paid Subscriptions."
And, don't skimp on wire size. If you want to add an accessory deep-cycle battery, isolate it from the cranking battery using a diode isolator and reconnect the regulator sensing lead so that it 'sees' cranking battery voltage.
What of wire quality? I am aware of AWG/B&S standards and insulation types, but what of metal quality.. any standards on that? One person on another board was using heavy gauge audio wiring for his dual battery setup. Supposedly for better quality (I'm assuming a resistivity/impurity issue).
In a new unit of time... how many auxiliary sockets are you intending and why such a broad range of current capacities?