UPDATE: The Optima batteries have been exactly what we need. They were completely depleted during the shipping process and I was able to roll-start the truck and recharge both batteries and the auxiliary battery with only the alternator. I purchased a CTEK MXS 5.0 battery charger which I ran to the auxiliary batteries in the rear. I removed it and connected it to each battery individually and reconditioned them. The batteries work better than when I purchased them new. I reconnected the CTEK charger to the auxiliary battery. i use it when we stay at campsites that have power hookups.
I also purchased two 90-watt solar panels from Set Solar in Cape Town. The panels are made by set Solar and were half the cost of any I could find in hardware stores. I used their cables, connectors and charge controller and connected them the distribution panel which runs to the auxiliary battery. I had Lowveld Canvas in Nelspruit make a case for them so I could carry them on the roof rack. We spent 5 days at Beverlack (north of Cape Town) over the New Year. It was very hot and I ran the fridge for the entire time and only hooked the solar up during the day. The panels kept the batteries charged without any trouble. I am pleased with the solar setup we have, the battery charger, and the dual battery setup from IBS. My auxiliary is a 55 AH battery and in the future I may upgrade it to a slightly larger version.