I'm thinking of MINI for Tiny so it could be something like MINIBUS? Don't know what the temp is - it made me think of temporary, hence transient which made me think of TRANSIT. MINI TRANSIT VAN or something on those lines?
Yes, of course, emf. Once I saw your answer, there it was: a sub = a temp. I didn't make the most obvious connection. Aarrgh! I had the answer and didn't know it!