Attachment 164498Update - I decided to cnx my order for a mud flap. After reviewing what I am going to do (fabrication), the bottom plate that the scooter (in reality, small motorcycle) will rest on is level with the bottom edge of the rear end cap/bumper.
Because of that and the angles involved, the rear end vortices will probably make the scooter dirty, ... over time and the mud flap will not aid in preventing anything like that. I do not think that the flap is needed to prevent any thing from hitting or accumulating on the scooter itself because rocks, debris, ... will probably go further aft and more significantly, lower than the scooter's attachment location.
The only benefit of adding any protection would be to traffic following to close.
Photoshop image of what initial design will be - Once I am finished, I will update again.