Expect the battery to be dead. There should not be a problem disconnecting the negative battery cable on your truck but on newer ones, and especially on Volkswagens, BMWs, and General Motors products, you do not want to disconnect the battery or let it run dead. Those dealers make a lot of money from the tricks those manufacturers designed in to cost unsuspecting owners money after the sale. Tow trucks and unlocking computers and radios are expensive.
Because of all the computers and their memory circuits, the industry standard is a good battery will start the engine for up to three weeks. After three months the battery might not be completely dead but it won't crank the engine. If there's no under-hood light to drain the last ounce of life from the battery, you might get away with recharging the battery at a slow rate for an hour before you try cranking the engine.
You can also look for one or two fuses to remove to turn off non-essential computers. On Chrysler products that is called the "I.O.D." Fuse, (ignition off draw). Haulers use them to allow cars to sit for many months in parking lots until they're sold to a dealership.
Some people run into trouble with old gas, although I have an '80 model and a '93 that rarely get driven and the gas in them is over five years old. They both run fine on that old gas. You might want to let your tank run low, then fill it with the fresh stuff when you start driving it again.