Hi Bruce,
Before you drill any hole in a surface, metal or glass, you may want to make sure there are no electric wires or hydraulic lines behind that area. Placement of the extinguisher is a tradeoff between accessibility of use and temptation for a passing thief. That's why you see some folks mounting them slightly out of the line of sight of a casual passerby. Wherever you mount it, practice a few times removing it, so that your first removal won't be under emergency conditions.