Hello Brad Buchanan,
Nice set-up. Your lights are powered by the alternator. It has 2 circuits, one for the battery and one for the lights. The light circuit is usually unregulated A/C output. I guess you are going to use 12vdc lights. Your alternator charging two batteries may not be enough, but you'll find out when you use it.
Adding the batttery means you want to use the lights for a long period of time. You may look into led's.Plenty bright, and very little power consumption.