An interesting idea. I haven't rented storage space in a long time so I don't remember what the rental agreement said, but wouldn't most storage facilities prohibit the storage of things like flammable fuels? Fuel would probably be the most critical item during the actual evacuation phase, as you point out, since you're actively using it up while driving.

If your storage facility is within the evacuation zone or "close enough", then it might be locked up tight to minimize the chance of theft, while the staff itself evacuates. Even self-service gates/doors may be locked down. Then you would have to break in to get your additional supplies. I can picture the news coverage now, "Mr. So-and-so is arrested as the first looter of Hurricane X, at a storage facility outside of Somewhere, USA, even though the hurricane is still 24 hours from landfall..." <img src="/images/graemlins/wink.gif" alt="" />