Airbnb Guest to Short-Term Tenant

[Inga Fonder]

I would like some advice about a current situation that I just experienced. There's currently a guest staying in a private room in my home that was booked via Airbnb. They've been here for a few days, and inquired about making arrangements to stay in my vacant unfurnished room with an air mattress. 

The person will be traveling on and off for the next 3-4 months, and wants a place to crash when in town. Since I don't know when and how long they'd be staying at the house when they're here, would it be best to set up a month to month agreement with a flat rate? That way, I get paid upfront, and don't have to lose income opportunity by blocking off dates that end up being vacant. Plus, there would be a written lease agreement as a security measure.

Would there be a better alternative to going about the situation?

I appreciate any input.