I found airtight capsules exactly right for the Criptoe Guldencoin. You need to make the hole in the rubber a little bit bigger, but than you'll have an pretty show and protective case.
I want to order them, but maybe there are more peeps in the NLG community who want one.
It's €2,50 per capsule, I wish to ship them all to my address and from there distibute them further. In order to keep the price as low as possible, the more the marrier
Please PM me with quantity if interested!