Hi Scott

you shouldn't charge your packs from you truck. Your truck battery probably isn't a true marine deep cycle battery. Starter batteries aren't designed to be discharged in this way. You'll wipe it out in pretty short order. Buy a real marine deep cycle battery or a generator to use as a power source.

I don't think you need to worry much about the IR unless the values start to consistently climb and reach near 10. That's about the point that they start to really nose dive.