I usually wrap one or two turns of black electrical tape around the mast, then lay the coax against that, and make about two or three more turns of the tape. This pads the cable a little bit, and allows me to then use a black (UV-resistant) cable tie over the whole thing. The outer layers of tape keep the cable-tie from putting too much pressure at one spot on the cable, which would deform it and cause a reflection in the signal.