From a physical perspective, the Google Search Appliance is not all that secure. I won't go into details, ahem.
Compile the source code where you can. In Python, you could be delivering .pyc files instead of .py files, which would at least deter casual intruders. I'll bet there's an option somewhere to compile the code to something even better.
However, when it comes to the physical end, you're a little helpless. Glue it all shut?
Take "Chassis intrusion detection" -- okay, so intrusion has been detected. Now what? Do you report it somewhere? Hard to do if the cable is unplugged. You'd have to establish a queue wherein that intrusion notice just sits around until it is delivered to your home system.
Are you going to be out to physically examine the machine every so often? You could put a big old wax seal on it. I'm not entirely kidding, perhaps a special tape with your company name on it might do.
Perhaps one of the people from Make could help you craft, in a larger chassis, some kind of lever or strictly mechanical device which, when the chassis was opened, press a very large magnet (labeled "ANTI-INTRUSION MAGNET") onto the hard drive. The steel hard drive chassis would make all but the most powerful magnets less than optimal, so you could maybe make a "window" for your hard drive chassis (yes, this has been done).
Most ridiculous scenario: cover the case in "WARNING: THERMITE-ENABLED DRIVE DESTRUCTION -- PLEASE PLACE SERVER ON BOTTOM OF RACK" stickers.