The walls of the freezer get HOT when it's running. The easy thing to do is to plug it in and feel around. Where ever you feel "warm" you will need airflow. On the ones I have here one of the hot spots is the wall just above the compressor.
Since you will need fans inside the freezer as well as outside, having 12V running around is pretty much a given. I'd run several small / quiet / cheap computer fans rather than one big / expensive / noisy 110V fan.