You're worried in Missouri? Silly boy. I'm stuck up here in Wisconsin winters. My buddy has three Dodge diesels that he rebuilt after they were smashed. They all sit outside and are never plugged in. He uses one for snow plowing, and one for long trips because it gets better fuel mileage than most minivans. I've seen these things start at 20 below.
What you do have to watch is how long you let it sit. Unless specified otherwise by the manufacturer, the industry standard is 35 milliamps is the maximum current allowed to maintain all the computer memories. At that rate most batteries will remain charged enough to start the engine for three weeks. I don't know how that correlates with diesels. You most likely have two batteries and they're pretty big. You don't have more computers so logic would dictate you should get well over a month without starting the engine. Keep in mind too that you need to drive the truck to recharge the batteries. AC generators are not very efficient at low speeds so just letting it sit and idle might not keep the batteries up.