DO: Fill it with full kegs of beer
Don't: Let the last one get empty before your next batch is ready!
Seriously though,
I would put a collar on it. It makes it easy to mount taps directly to the front of it, or it gives you an easy place to drill holes for lines to get out. This way you don't have to worry about hitting coolant lines in the side walls.
A collar also gives you the ability to put kegs or CO2 on the hump, if the collar is tall enough.
Can you post the make, model number, and dimensions? I'm building a database of freezer inside dimensions for people who are building keezers!
Thanks!