I have two toolboxes that look like the picture below, with handles which lie down but still make a "bump" about a 1/2" high in the middle of the top so I can't make a stable stack when not in use. I'm considering doing something to make up the height, a ridge along the ends of the bottom of the top one. I was thinking maybe I'd epoxy a short length of 1/2" tubing. Any thoughts?
Alternative: n the lower chest, remove top handle and add side handles. You might also want to design something so the two interlock, to prevent the top case sliding off too easily.