Our garage is sloped where the ground is higher at the wall edges and sloped down in the center where the drain is--which is right underneath my car. When I have to go to work right after a heavy rain I have to take a big step to avoid walking in the puddle getting into my car.
But yeah, even with the freezer being at a higher level, when that rain comes heavy it could possibly seep to that back wall, which is why we put it on the pallet...bricks would have been good, too, we just didn't have any and the pallet has held up well. It's a smallish chest freezer. I want one of those taller ones with drawers in it eventually.