If anyone is looking for a clear cut guide on the basics of RFID systems I found thisto be particularly helpful: (http://rfid.atlasrfidstore.com/hs-fs/hub/300870/file-252314647-pdf/Content/basics-of-an-rfid-system-atlasrfidstore.pdf)

The table on the last page lays out the pros and cons of different options very clearly. 

Donal O'Sullivan , Interesting idea! Have you thought at all about what type of RFIDs you would use? I think passive RFIDs would be the go to, but then you would need a fairly high powered antenna that wouldn't be disturbed by the interference caused by the freezer. Any thoughts?