Problem with lag is, you can make you script as secure as possible, lag is still able to break it. I used to ignore the chest when I had the feeling the server lagged only a few miliseconds.
I don't think there is a 100% secure persistent storage system and maybe there shouldn't, however to extend on Kermit's idea I found this script on the vault:
http://nwvault.ign.com/View.php?view=Scripts.Detail&id=35, apparently it stores your cd-key on the chest and keeps the stuff for ten minutes, only characters with the same cd-key can open the chest, f you haven't emptied the chest within 10 minutes it will self destruct and spawn a new chest for others to use, seems like an excellent transfer system to me. Only problem is the script is quite old and I can't test it for you guys, so if anyone has the time.
Also you might want to look at the following persistent storage scripts:
http://nwvault.ign.com/View.php?view=Scripts.Detail&id=1214http://nwvault.ign.com/View.php?view=Scripts.Detail&id=3049http://nwvault.ign.com/View.php?view=Prefabs.Detail&id=653They should still be tested though