I have a possible solution for you, however, we do not carry tonneau bed covers for your Yamaha Umax Golfcart / UTV.
If you just wanted the cover for looks or to keep the cargo inside the bed, you could look into the universal Erickson Mesh Tarp and Truck Bed Cover - Heavy Duty - Black - 6' x 8' # EM57056. Keep in mind, this is not weatherproof, but is made of a mesh material to protect the cargo from sun and wind. I have attached a photo showing this cover being used on a small utility... view full answer...