Will a Rockmite fit in an Altoids tin?
Sure does! And you won't have to cut out holes on the top or bottom of that nice tin.
If someone does have one of the ATS rigs (well, not the ATS4 - it's too big!) you can actually put it in an Altoids tin without cutting the holes in the top or bottom - see what I did to preserve the lid of my "Sindy" tin that I used for an ATS-3b: http://www.aa4ga.com/2012/04/steve-webers-ats-3b.html
That said, if you can find a Weber MTR, they are the best QRP rigs I have see, and built!
I'm using the KD1JV MTR case for my MTR instead of an Altoids tin - much easier and nicer looking, as well as more robust...although a little bulkier and heavier. But the case was not included in the first run of MTRs, so that would be something to ask about if you get one on the used market.