Don't store your knife in these cases! They are excellent for transporting knives, especially folders in the closed position. Fixed blade knives tend to cut the liner to shreds as the knife moves around during transport.
The problem with these cases for storage is moisture, as you surmised. I have had more than one knife get the dreaded spots when stored for very long in a closed case. Same goes for guns in gun rugs. You can minimize problems by spraying the inside of the case with silicon spray, and making sure that your knife is protected with a full coating from tuf-cloth, renaissance wax, or similar. But the best knife storage allows air to circulate around your knife, and this is not possible in a closed case.
