Considering that these are probably very valuable coins, both in bullion value and collector, have you ever thought of slabbing them? I'm not suggesting it but just curious as to your opinion. I'd think that slabbing takes the guess work out of it for others as far as authenticity goes, but other than that I know gold is inert (alloys of course not, but relatively inert then)
It's kinda funny that for gold, you have to worry more about the coins damaging the storage system than the storage system damaging the coins. Pretty much just keep them away from PVC and they'll be fine. Even then, gold might laugh off PVC (but I wouldn't take the chance).
Actually, I have seen coins that were slabbed, later found to be fakes. Good examples were some fantasy "Elephant/Fish" AV Fanams from Mysore/Medieval India. Also Kunker and other European Auctions seem to downgrade slabbed coins, since the US grade is inferior to stricter UK/European grading system. A Czech auction recently pulled a Josef I 1/4 Dukat that was slabbed.....fake. I think as a whole, European auctions seem to be way better at grading/guarantee of authencity. Third...coins look way better in flip/ more clear image of coin/takes way less room for storage. John