On the liability waiver thing, the waivers are almost universally used, and then almost universally ignored by attorneys when filing liability lawsuits. It is almost universally accepted law that a liability waiver will only protect an owner/operator in the event that a licensee (person using the property with permission) is injured due to the normal use of the property or their own negligence. Think in terms of paintball facilities. If a player is running across an open, flat field and trips, the injuries are related to normal use, and the waiver should help. Or, if the player takes off his protective mask during the course of a game and gets injured, it's his own fault.
HOWEVER (all caps to get attention), every personal injury lawyer out and about knows that you always allege that the owner/operator was negligent in the operation of the business in some manner(s) so that they can jump right past that waiver and get beyond that initial motion to dismiss that cites to the waiver. Is the waiver useless? No and yes. Not useless as it will help to get rid of some claims, but it won't stop you from getting sued.
So, on the rent-a-garage scenario, a waiver will help get rid of the lawsuits from the guy who sues because he smashed a finger while trying to break loose a rusted bolt using his own tools or misusing the shops tools. But it won't save you from everything.