Using some filler primer at the priming stage may help as well. I also tend to get a little bit of tube fraying, no matter how carefully I sand. Once you get some primer on it and a couple coats of paint, it is not very noticeable, if it is still even visible at all. You can also make a defect like that visually disappear by putting a dark-colored ring around the top of the tube, too.
MarkII