Tim....I make the club rent the rig from my company and a separate transaction for the engineer. Sometimes the sound engineer will rent the system from me. While the system is under the care custody and control of the leasee the bailee's coverage of their general liability policy is in effect. This is business 101 (well maybe 301) but seriously why would you not expect to be covered?
Bob's situation is different from yours. Also, are you remitting sales/use tax on the rental part of your agreement? Are technical services subject to sales or use taxes in your locale? I ask for several reasons, one being that most folks don't know about it and two, many of those that do simply ignore it.
My experience with providing sound in bars is that you can have a contract, but you'll never get a dime for things like this. My cynicism is well earned, too. Details later.