Best advice I can give you: Store your car on a large drop-cloth, rather than naked concrete. Concrete is porous and can let moisture up. Use a plastic dropcloth as a vapor barrier.
Other tips:
Get the car as clean as you possibly can... inside and out. Yank the seats and the easy to remove carpets and clean under there.
Put drip pans under your engine, transmission and master cylinder. Leaks spring up... uhhh.. down.
If you don't have a sealed Optima-type battery, then just remove it from the car. Wash that area with a baking soda solution, then rinse and dry well.
I agree with draining the fuel on storage more than a year.
I've heard that some people put mothballs in the tailpipe and cover it with windowscreen material. I would probably do the same with the air filter.
Also... make yourself a list of all these "storage tasks"... and put it on your dashboard!! That way, when you come back to your car, you remember what you need to reverse before you drive it!
Be safe and enjoy your extended trip!
Cheers,
Lawrence