Thanks Dave, The reason I want to make one in-house is cost. This is not a standard part and after contacting a couple of vendors ($1,000 plus for first tray) I decided it would be much cheaper to do it in house with our CNC.
One problem with a metal tray relating to ESD is its conductivity. Most trays are conductive but have resistance or a disipative nature. If you were to place a "charged" component into a metal tray that had an uncontrolled path to ground you would shock the part from its discharge into the tray. You can load parts with the tray on one of your ESD mats and then you don't have to woory about it.