I'm planning a small bathroom install (40 ft sq) and would like to install in the shower area. According to the SunTouch site & Install manual I need WarmWire with a 'W' designation for the shower area (120040WD). I see a very similar kit at Home Depot with a slightly different designation (120040 R). Can I use the R designated cable in the shower area? If not, where can I find the WD designated cable kit?