I have never seen one but you could make one that attaches to the rear part of the seat but you would loose the passenger area when its on. or you could make one that bolts to the grab bars on the sides. either way its something you will have to make at home. if you give it a try take some pics and do a write up for the forum, you might stubble onto a great mod. there aren't enough mods up for the people 250 scooters.
