Does anyone know of a template for the location of factory XM antenna? Or... does anyone know of an aftermarket, low profile, permanent mount antenna that can be placed on a flat section of the roof? My truck didn’t come with Onstar or XM, but I switched out my radio module for one with XM, the only thing I don’t like is that it came with a magnetic antenna. If I went with factory shark fin; what part number would it be? If you look at the part online there are options for Onstar, satellite radio, and digital radio...I only have XM, no Onstar.