According to the website, the backrest has to come off. I would guess they are using a pad on their top boxes...if they use it while riding 2-up. I have the Givi adaptor on the Honda rack so I don't have to remove the backrest. I haven't used the trunk yet though, but it is ready incase I ever need the extra space. The main reason I went this direction is because I already had this set up on another bike, so it was the simplest/cheapest solution for me.