I wouldn't assume that there aren't coils near the top. You might try the cornstarch method to see if you can figure out exactly where the coils are on your freezer. You might also want to drill a small pilot hole that just pierces the skin of the freezer, and then use something to feel around in the foam to make sure there aren't any coolant lines or wires where you're trying to make the hole. When you drill the full size hole I'd also just drill through the skin, and then cut/pick the insulation out by hand just to be sure.
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