Renting out a cargo box. How to make a contract and policies?

I'm a deep reenactor and bought a cargo top for my Subaru, and seeing all the rental ads on Craigslist has me realizing I can use it for that the other 51 weeks. I'll need a contract of some sort, ideal policies for security deposits, and other odds and ends...Has anyone done this kind of small time rentals and have advice?