Here is what I did on my Tubus Logo EVO before my trip last summer. PVC plastic tubing, slit lengthwise to put over the rack tube, then wrapped electrical tape around it in several spots. Some people that used the same tubing as I did used zip ties instead of the electrical tape.
I am in USA where we still use inches and miles and other outdated units. I am not sure but I think the tubing dimensions were 1/2 inch outside diameter with a 1/16 inch wall thickness.