Go to the auto parts store and purchase a rectangular convex mirror. The larger the better. Then get yourself a right angle shelf bracket at the hardware store. Using double sided "3M" mounting tape (it's made for external use on vehicles), attach the mirror to the shelf bracket, and the bracket to the leading edge of the pin box. Adjust the bend so that you can see the hitch as you back under the pin box. Problem solved for about $15. I used this system on my previous fiver, which had no factory installed mirror, for years with great success. There are similar commercial pin-box mirrors made for this function, but they utilize smaller mirrors, don't work as well, and cost a lot more.