What is the best skin/film to protect the back of the iPhone 5? I'm not too concerned with the front, but want something for the back...
Wow, that's backwards.
This may be all you need. The Spigen Ultra Mix Front and Back Protector.
Spigen has always been reliable for me, if that doesn't seem to do it for you, you can also check out **********.net for back protectors that are in carbon, metal (sticker), or even leather. I also bought the metal series from ********** to try them out, however, I will warn you that they will take a while to get to you.
Those spigen screen protectors are really easy to install. I'd just recommend you have a extra roll of tape handy in case the dust removal stickers don't do it for you, and also take your time. What sucks though is that Spigen is only giving you one set now, they used to give you two.