There are more than a few good tutorials out there for NMM. Where the light and shadow falls is a bit different that what you'd expect sometimes, though. Look at a real metal object that is straight up and down. You'd get those sharp highlights on the very top edge, but thaty wouldn't come down from the top on side of the door. The highlights there would actually be at the bottom of that vertical face, fading up to the shadow.The tanks are coming along nicely over all. Keep it up.