[DonVoigt]

I have seen more guns "ruined" by storing them in zipper cases than I care to remember.
When stored in a zipped case- they can't breathe- i.e. exchange air to eliminate moisture.

If you must store in a case, leave it unzipped, a nylon or other sock is better. Keep in a cool, dry place. The storage area really should be climate controlled, like a house with ac and heat. Not in an attic or basement or un-occupied house.

Safes are the same way, they should be in a climate controlled area or must be provided with a heat source in side to keep condensation away. "Drier" units are also ok for a safe if properly rotated and "re-charged or is is de-charged".

Of course oil the metal before storage. If you are going to store the luger long term and not in a well controlled environment, I'd also remove the grips.

JMHO, based on 50+ years of firearm storage and use.