Thank you Barkbark, there really isn't a lot of room there to add a mud guard over the rear tyre without it hitting the boot liner under full compression. As the cut outs to the side are asymmetrical to allow for the belt drive on one side it would be difficult to attach flaps hanging down either side to help much, and the exhaust also needs to be avoided on the other side. Looks like most of the road dirt and spray seems to be at the rear and front of the tyre, it may help to design a couple of covers made from a woven nylon material that would absorb the water droplets and help protect the fuel tank filler, exhaust and inner body structure form dirt and stone damage.
