Fully charged pair of 6 volt batteries in good operating condition should last at least 2 days, longer if you are frugal with your power demands. Yes, you certainly could hook up to your truck and give a little boost to your battery and help bring in slides or powering jacks, although not an ideal or efficient way to recharge battery bank it will work in a pinch. Converting to LED lighting is a great way to reduce overall power consumption.
If you decide dry camping is something you want to do more of in the future adding a bit of solar could keep you from investing in a generator right away. If it amounts to just a couple outings a year you could get a Renogy 100 watt portable suitcase solar panel (under $300) that includes a charge controller and readily connects to your battery. With good sun it can easily extend your dry camping and even allow light TV and furnace usage. Happy Dry Camping!!!