It's very simple for either Cb or radio antenna. Of with the saddle, unscrew the trunk cubby pockets, the Phillips screws are inside the trunk. Unscrew the trunk trim pieces that the antenna will bolt through. The markings for the holes to drill are faintly marked on the inside of the trunk.
This article covers the gl1800 but gives an idea of what needs to be done. http://www.goldwingfacts.com/1800CBantenna.htm