My advice is to be cautious of drilling the case close to the sealing surface. Then be even more careful tightening the tapered pipe fitting with the hole so close to the case edge/ sealing surface.
pipe threads will wedge the surrounding material with the fitting, and there is a recommended wall thickness surrounding the fitting for different materials, but i don't know where my chart for that is. if you have one side of the surrounding material much closer to the edge of the hole [think of a very offset hole], the wedge effect will concentrate on the "thin" side more than the "thick" side, promoting a crack to form. also, most seem to have a tendency to crank on pipe threads so they don't leak.
