|Cross-country skiing in Skarvheimen, Norway. Photo: Bjørn Sandvik|
Open the route in QGIS, right click the layer and select "Save As...". Select "GPS eXchange Format [GPX]" as the format, and "WGS 84" as the coordinate reference system (CRS). I'm also skipping attribute creation as my line only contains coordinates.
QGIS saves the line as a GPX route. You can import this route in Garmin BaseCamp (File -> Import). Give the track a meaningful name.
My 500 km route consists of 3867 points, but most Garmin GPS units are only capable of showing 250 points per route. You can get around this limitation by converting the route into a track. Right-click the route in Basecamp and select "Create Track from Route".
Transfer the track to your GPS unit:
You should now find the track in the "Track Manager" on your GPS. Select "View Map" to see it and then "Go" if you want to navigate along it. Depending on the maps you have on your device, you can also display an elevation plot. Since the original track don't contain elevation data, the GPS will try to fetch it from your map.
My GPS is now loaded and I'm ready to go!
All data are available on GitHub.