A few thoughts...
You may want to talk to DSI, RFGEN, RFSMART, Science Applications International Corporation (SAIC), or Cribmaster. All of these guys have experience with barcoding/RFID.
It's feasibly possible. The problem is the upfront costs. For example; for that size of storeroom I imagine you're going to spend between 100-150K for a single storeroom application with a signle portal. That will probably include 15-20,000 passive RFID tags.
However, your inventory visibility skyrockets when you introduce one of these systems.