Always looking for another project, I decided that I would flush mount my Garmin 196 to make the panel layout work better. Before it was mounted on a RAM arm mount, which tended to vibrate at certian engine speeds.
To mount the GPS to the panel plate I simply made some U shaped brackets that hooked into the finger holes on each side of the GPS. I decided not to make it easily removable as I only update it a couple times per year and will just remove the plate with the 4 screws.
To get the cutout sized, I opened the GPS by removing the 5 screws on the back of the unit. That allowed me to split the case and use the front half as a template to get the proper shape for the cutout.