The evaporator lines are usually just behind the inside metal skin and the condenser lines just behind the outside metal skin. You MAY be able to tell from the temperatures when it's running where both sets are. Once you do that, the method with a small, pilot hole as mentioned by JuanMoore above would probably work.
Have you called the manufacturer's tech support department? They may have a decent drawing or tell you where there is a definite location free of any tubes / wiring.