tmp:/ system space is variable depending on how many channels you have installed. If you are using the space, you will need to manage it while your app is running. When your app exits, the tmp:/ space is cleaned up.
I guess I'm looking for guidance on how to manage it. My first thought was to check for available space before writing to it, but that doesn't appear to be an options. My current line of thinking, which I haven't had a chance to test, is to attempt to write, verify that the write worked, clear out space if it didn't, and then attempt to write again.