TDI's are very resourceful. Keep in mind the 2015's that were held by VW pretty much sat on dealer lots for 2 1/2 years before allowing to be sold. VW had to maintain the battery, Had to drive/run them once a month, and changed the oil, dsg fluid, wipers, and tires when they were sold.
So- lets follow that course:
Chances are youre storing it outside. The key issues: Battery, fuel and rain drainage.
Clean out the tracks on the top/sides of the trunk and hood where water drains out. If you have leaves or gunk blocking it, then the rain may seep into the trunk or other areas of the car.
First- Park on a flat, level surface. This ensures rain drains freely. If you have a sunroof, make sure the sunroof drains are clear, blow them out with compressed air.
1. Fuel Tank: There's a reason VW doesn't fill the new cars stored at the factory with more than 1 gallon of fuel. Fungus-- Use an Anti-fungicide: Drive it until the low fuel light comes on. Pour in a 16 oz bottle of Power Service Bio-Kleen to the fuel tank. Drive it until the miles till empty are less than 20. This will ensure the fuel lines are protected, and the fuel pump is protected as well.
Oil: Change your oil a week or two before deployment, and do the fuel filter as well. Fresh oil wont have the acidic build up of older oil, and that's better for the internal components of the engine since it's not circulating.
2. Hook the battery up to a trickle 2 amp charger if you can plug it in. If you store it outside, there are some cool solar panels that you can buy at Camper World and on Ebay that trickle charge the battery through the cigarette lighter/ 12v plug. you can leave the solar panel on the dash, plugged in to the 12 v plug.
Returning from deployment:
1. You'll have flat spots on the tires. Noticeable by the thump, thump thump sound. They will go away after 10 or so miles of driving. To minimize this- air the tires up to the Max rating on the sidewall. Then add 5 lbs. (Generally 45-50 psi). be sure to depressurize after a day or so.
2. When you start it, it will have zero oil in the engine. All oil will have drained to the oil pan. Start it, let it run for 3 seconds and shut it off. Repeat. 3x. This helps splash a bit of oil around the engine, bearing and camshaft. Any oil that comes out of the oil ports is good. A little lubrication is better than none, and 3 cycles of 3 seconds each will allow the oil to lubricate the bearings and camshaft. Even if not at full pressure, it will help with dry start wear and tear.
3. Refuel as soon as possible, and drive the car until the oil temperature reaches at least 212 to burn off the water vapor in the oil. 20-30 minutes of driving should do the trick.
That's pretty much it.