I originally put the CO2 tank inside the kegerator for minimal footprint. There are two problems with this - regulator access means moving kegs out of the way, secondly the CO2 tank being cold drops the tank pressure.
There will have to be a follow on project to hide the tank somehow, the utility benefits don't completely outweigh the loss of aesthetics.
Step 1: Tools List
18" x 5/16" drill bit (3/8" would have been better)
Step 2: Find Safe Location to Drill Hole
Hitting a cooling line inside the refrigerator wall or cooling plates inside the refrigerator is to be avoided. I settled on the final location by googling and checking with hand for absence temperature difference (indicating a nearby cooling line underneath the metal skin).
The drilling was done inside to outside, to provide near clearance to the cooling plates and other hardware. The long drill bit made this job very easy, I could see a problem using a shorter drill bit as the walls are thick and not much room for drill clearance.
Step 3: Finished Hole
The hole was drilled 5/16", I had to open it up to around 3/8" for free clearance. TheC O2 line was pushed through, outside -> inside then connected to gas T.