Do you have testimonials from happy tenants? Can you offer them a bounty for referrals? Are you members of the chamber of commerce so you can get in front of businesspeople who can help you virally?

Have you looked at your facility from the outside in, like a customer, and asked "what would attract me, what would I expect from a storage place?" Focus your marketing efforts on that answer, provided you're not already doing that, and please forgive the preaching to the choir if you are.