Leasing garage storage units in St. Louis, Missouri

[Max Householder]

We just closed on our 2nd property which includes a garage split into 4 storage units each with their own roll-up garage door on one end and steel door on the other. The previous owner had been renting them out separately, i.e. not to the apartment tenants. We would like to continue to do so for added income as here in St. Louis City, storage in these older properties is quite limited and there seems to be a solid demand for extra storage units. 

Does anyone have any experience renting units like this? I'm looking for tips, best practices, a lease/document you use, do you typically shoot for 6-12 month leases or just month to month from the start? Do you run a background or credit check or take a deposit?

Two of these units are leased but the tenants have not paid in 2-6 months so I am also looking for insight into storage unit tenant laws and how I go about evicting their stuff for non-payment? Any comments are welcome. Thanks BP!