My current idea for the project enclosure involves a Pelican 1120 case, which is about small enough for a kindergartner's lunchbox. I think it would be the perfect size for an Arduino, 9V battery, a few breakout boards, and the RTD itself.

The Pelican is also waterproof, so I could leave it outside during rain (for instance) without fear that it would get damaged. I'm thinking all buttons and switches would be inside the enclosure and I would open it up to make any changes to the settings.