Having stored two cars regularly for 15 years. I would add the following to the link above......
If outside you have to watch covers for chaffing the paint, particularly sharpish corners. But I wouldn't leave it outside anyway for two reasons, dampness and a tempting target given the value.
Inside, I just use decorators clear film dust sheet pinned down by a couple thick newspapers on the roof and another couple on the bonnet. Stop the wind blowing off the film if the garage door is opened. Here's one cooking at the moment since last October......
Capture.JPG
Modern tyres don't appear to deform the same as old ones did. Just add about 5 psi to the inflation pressure recommended by the tank flap label. Over inflating modern tyres can end up with tyres bursting the interal tyre's strengthening bands through the rubber (Been there, got the badge
)
I don't ventilate the car cabins with a slightly open window. Instead I use a large moisture trap like these which last about 6 months between refills.
Moisture Trap for Corrado - Scirocco.jpg
Then once a month, pump the brake and hydraulic clutch pedals 5 times each. This stops the rubber pipes from deteriorating. Hand brake is left off and the cars in gear with the wheels chocked with wood blocks.
Not into running an engine during storage. So I turn mine dry with the fuel pump relay removed. I spin a dead engine on the starter in 4 by 20 second bursts with 30 second rest periods inbetween. Do this, along with the pedals exercising above once a month. Not sure about a diesel engine as both of mine are petrol. On a diesel Scirocco you could pull Fuse 27 (Blue, 15 amps) in the side dash fuse plate to isolate the Fuel pump, Fuel Pump Controller and Glow plugs. (You will have stored diagnostic fault codes possibly as a result though).
I also use an "intelligent" trickle charger perminently connected to maintain the battery voltage (Disconnected though when turning the engines to prevent damage to the chargers). A decent charger will restore the battery back to being charged within a few days after you have turn the dead engine over.
I also use a de-humidifier from October to April each year. (Good source of "clean" water for washer bottle and coolant changes). Stops the brakes from rusting (and presumably the clutch plate).
Store with only about 15 litres of fuel in the tank, so that when they come out of storage, I can fill up with fresh fuel. Given its going to be 12 months, you might consider a diesel additive to help stop deterioration and stabilsie the fuel.
C.