I tow a heavily loaded Rubbermaid bin secured only by bungee cords stretched over the top when I get groceries and it has never moved an inch. Assuming that the footprint of your kennel is smaller than the dimensions betweens the tubing on the trailer, the kennel will sink down below the level of the tubes as the floor (the reinforced vinyl or whatever it is) of the Flatbed flexes down. If it's bigger and will be sitting on top of the tubes, you will want to anchor the kennel more securely (easily done with some nylon straps).