Hi Aamil
Welcome to the boards!
If the case is not air tight there is always a chance of corrsion. Generally,
good quality silver (and gold) coins do not corrode though a
patina can form over the years. If bad
quality (ie. an
alloy), a
fouree or
plated then of course something bad could occur.
Bronze will corrode though many coins have a protective
patina already formed which will
help.
A case will be great to protect the coins from physical damage though if the coins move around inside whilst you travel it may not protect them from rub wear.
Hope this
help - actually other articles already in this section on this if you look through.
Brgds
AlexB