Your standard auto or general liability policy will not cover you for towing operations; you need specialized coverage.  These coverages include:

• Liability, bodily injury — covers you for injuries to other persons for which you are held responsible.
• Property damage — covers you for damage to other persons’ property (NOT including the vehicle or other thing you are towing) for which you are held responsible.
• Cargo – as a hauler you can be held liable for theft of or damage to a vehicle you are towing, including while your rig is unattended, is underway, or during hookup operations (ofter referred to as “on-hook towing coverage” for towing operations).  If you store vehicles, boats, or other things you also need coverage for garage operations. Your cargo coverage must be written so as to provide coverage for all of these things (also see separate article on cargo insurance).
• Ramp, chain, tarp, and binder coverage — if applicable to your rig; covers these items for fire, theft, vandalism, and damage suffered in a collision or rollover.
• Constructive total loss or diminished value — If you tow, for example, a new car or boat and damage it along the way, the dealer might not be able to sell the car or boat as new anymore, will sell it at great loss, or will sell it as scrap!  On the other hand, a standard cargo policy might only pay the cost of repairing the vehicle or boat, which might be much less than the reduction in price that the dealer will suffer. You could be held liable for the difference. This coverage protects you.
• Over-height loads — Covers you if you damage your load while driving under a low bridge or other structure.
• Collision — covers your truck and trailer for collision with another vehicle or stationary object and for rollovers.
• Comprehensive — covers your truck and trailer for fire, theft, vandalism.