We always used a shop fabricated bracket and mounted it as best we could to be in the correct location and secure. It actually worked good, the braket was just a 90degr angle with sides and we put the template on it and mounted away to the floor of the cabinet. Also the detector must be upstream of any fresh air or make up air by code. So this location cant be used if your duct system uses any of these, it will have to be duct mounted. As long as it is in the airstream and the sample tube is oriented correctly it really doesnt matter exactly where, and as far as the manufacturer its more an afterthough and they problably didnt allow for it in the design and therfore no holes.