There are clear polyester films, such as window tint, model airplane film (iron-on), and films made for the bottom of cars to prevent damage from road gravel.
Urethane car paint is tougher than about anything, but it's expensive because it requires a $25 catalyst. For about the same cost, you can probably get the case powder coated, but all the existing paint has to be stripped off first. Powder is so tough that if you hammer it, there's a good chance that metal will come off the hammer. It comes in different types - epoxy, polyester, acrylic, and polyester is probably the best choice.