Just learned something kind of cute.
You can create a map showing the route of a proposed trip in Google Maps, save it under a descriptive name to their MyMaps function, get the URL of the page that shows that map, and then go to TakItWithMe to create an uploadable file for your GPS to use when mapping the route. Essentially, Google becomes the mapping software's brain. Afterward, you can delete the entry from Google, if you want.
Nice. Tomorrow, we'll see if it works!