All of mine have been in the factory boxes/cases for 23+ years and still look as they left the factory!!!
I have never had a problem with the boxes. Now pistol rugs.... That i have gotten rust after the range in like 3 days. I put it in there and had to work, just forgot, that made me mad.
Shouldn't be any issues if stored in a climate controlled environment.
Type of foam, open vs closed cell foam, makes a difference. Some of my HKs have been in factory boxes for 10 years. I put a dessicant pack in each and oil once a year or so. No worries, you'll be fine. You can also get Zerust tabs if you're really concerned.
VP9 - all 4 of them :-)
HK45 V1 German Made
HK45 V7 US built
HK45 V1 US built
HK45C V7 OD
HK 45C V1 German Made
Should not you keep them is safes?