Someone may have already thought of this idea before but I haven't seen it. I have always had trouble lining up my hitch ball to the boat trailer coupling so I thought a mirror mounted on the tailgate of my truck might work for me. It works great and I hit the coupling just right every time now. Here are a few pictures of how I did it. It is somewhat crude but I am into function here and it is quick and simple to make. I did cut the slot that fits over the tailgate a little bigger so I could put a piece of pipe insulation over the wood to keep from scratching the tailgate.