Last summer after I installed the top box I realized that when I was on the road and stopped somewhere, that if it rained, the nice leather on the back-rest of the top box would get wet. Unlike the cover for the seat that comes with the Vespa, there is no such offering to protect the leather on the top box.
Updated July 2014: We started to make and sell these but I have moved and the seamstress is no longer available. However, any local seamstress can make one quickly and easily. Just bring your Vespa to the store and they can measure the top box and show them a picture of mine.
Some people do not ride in the rain so would only need the cover with the elastic to hold it on just fine. But if you plan to ride in the rain, we recommend an additional Velcro that will latch underneath the top box to keep it on when you are riding. Additionally, we recommend to add a reflective stripe to the back.