A friend of mine left his old porsche in his garage for a couple of years. He recommends to:

- remove the battery
- remove the tires ( tire rubbers expire after some duration )
- sit the car on concrete blocks
- leave gas and oil inside ( rust appears if steel is dry )
- cover with fabric ( sheets will do )

Upon your return, you will need to drain the oil for particles especially in the transmission and engine oil, buy a new battery and tires.

Some rubber and plastic parts had to be changed due to decomposition such as door seals, window seals and the windshield wiper. You might want to remove the windshield wipers too.

Rats got to his wirings though. LOL!