Well, if you really want it weatherproof 
Get a short length of plastic tube (e.g. pvc conduit), cap one end, fill it half way (or more) with hi-temp silicone electrical (dielectric) grease. Mount it open end down on the mast, u-turn the spliced wires up into the tube so that the spices and ends of the cable jackets are well in the grease. Tape/clip the wires to the mast, stuff the open end of the tube with rubber/plastic foam to keep it clean.