there was a numberplate resivoir on mine when i got it ....probably the easy wa to solve the problem ......a little alloy mud guard bolte to protect the rsv ....works fine
now if you want to go cheap and cheerful ..a scotoil bottle held in a bycycle drinks holder will do the same job for next to nothing ..works fine on me klr
its just cable tied to the engine bars and stays put no problem ....i use chainsw oil at 5 quid a litre and with this 500 bottle full your good for 7000 miles or more