Brian it's easy to save a trip with S & T and transfer to the Garmin. That 7" model can use GPX files.
In S & T after you save your route, save it again as a GPX file. Plug your Garmin into your computer (USB cable comes with GPS) and copy that saved GPX file to the GPX directory in your Garmin.
When using your Garmin go to apps, then select the trip file that you saved and it will map your trip. What the GPX file does is really only transfers the vias and the Garmin uses it's own maps so some differences between S&T and Garmin route may appear. But this saves so much time then trying to try to route those vias in directly to the Garmin.