Avoid -- they want your social security number!
Great, if you are willing to give them your name, address, email, home phone, work phone, cell phone, employer, occupation, drivers license number and social security number.
The presumption is that you are a deadbeat whom they will have to initiate legal proceedings against if you don't pay your bill.
Sorry I don't do business like that.
Social Security number? To a self-storage company? You have to be out of your mind to give them that number.