Are you sure it's zinc? Also, have you checked the cud website? If you can find a matching known example, it may help to answer the question (of course a scale would do the same). Still, I see no reason why an airtite wouldn't be perfectly sufficient no matter the composition, and can see nothing about the coin that would concern me for long term storage.
Well I could not get the airtite open soooo, This is what I did I took a dime weighed it 2.34 or something then weighed a dime in the same airtight,Deducted, Weighed the cent in holder at 5.44 or close deducted the weight of the dime airtight and came up about 2.45, That is the definition of fuzzy math my friends!!
It's safe where it is as long as you keep it in a stable environment.......no heat, cold or damp extremes. Chris
Here... http://cuds-on-coins.com/lincoln-cent-cuds-no-date/ I wrongly assumed that they may have additional information on it, but apparently not. Still, check it out..
I cant wait till someone puts some of those back in the Wild. I have a few Cuds but know where as big as @abuckmaster147. Hope you heal well, Glad, you are sharing your collection. I enjoy seeing it.