Carefully drill a hole into your freezer for the probe. Take your time and drill the initial hole through the outside wall of the freezer. Once through the outside layer, stop drilling. Then push through the insulation until you feel the inside wall, and start your drill again. This way, you can ensure you do puncture any refrigerant lines that may exist.
"A fine beer may be judged with only one sip, but it's better to be thoroughly sure." -Czech Proverb