Environmental contamination on high voltage outdoor insulators can cause leakage currents and electrical flashover and finally reduce the reliability of electric distribution systems. To prevent energy losses and enormous damages, the in-service life of insulators has to be extended. For this purpose, room-temperature-vulcanizing (RTV) silicone rubber coatings are used due to their hydrophobicity. The objective of the current paper is to enhance the weathering resistance and proper adhesion of these coatings to the insulator. In the present study, adhesion improvement was achieved by adding titanium dioxide (TiO2) nanoparticles and silane coupling agents to the silicone rubber. The mechanical properties of nanocomposite coatings were characterized using the pull-off test method. Also, the water immersion method was employed to investigate the weathering resistance. The results revealed that adding TiO2 nanoparticles and silane coupling improved nanoparticle dispersion, adhesion strength, hydrophobicity, and weathering properties of RTV coatings.