A good means to standoff is the Radio Shack standoffs for 300 ohm twin lead that are about 7 inches or longer. Some screw into wood, or clamp to mast. PVC ones can be made. Home Depot sells electric fence standoffs in a bag of 25 for $5 or so. The rule of thumb is at least twice the spacing of the line, but since you are crossing at right angles, it is minimal interaction anyway. 73, Stuart K5KVH