Absolutely the very first thing you need to do when you find yourself anywhere near a 20 mil is to grab a 4-5 inch grinder with a cut-off wheel and remove those stupid lips that come up on the can above the bail whose sole purpose is to center the lid before closing. They don't even work very good for that, and if someone ever tries to open the lid like a hinged 50/30 cal., it bends that lip out into a katana-like blade that will cut you open quickedy-quick. After you get rid of those lips and file them smooth, duct tape (the black hundred-mile-an-hour stuff, not that gray shit) one of the bails closed to the side of the box and with only the slightest instruction or common sense you more or less have a "hinged" 20 mil.
And paint it! Whatever color the gov't chose for these things must have been decided upon which color could attract and hold heat better than black,…And they found it.