how do i go about loaning a car from my auto body shop?

[suburbanauto917]

I have three cars that I own and I own an auto body. Now I'd like to loan the car to customers that need rental cars. But I need to know how to go about not to list it as rentals. What kind of contract do I need to initiate this each time and what kind of insurance do I need? Can I go through their insurance company?