My kids love riding with me on the Ryker but no place to keep the spare helmet after dropping them off at school one at the time of course. So I added top case. I bought the top case from Amazon $56 shipped. I used 3/16 x 5" x 19" black steel. Little bit of cutting and grinding also some drilling, I was able to fabricate mounting bracket for the top case. My wife said it looks factory so that is good enough for me. Here are some pictures.
You could have saved yourself some trouble if you would just tie them to the back and make them run home from school behind you, like Chevy Chase attached the dog to his bumper in National Lampoons Vacation. They probably need the exercise after a full day of sitting in school being indoctrinated.