Update - I've just tried the method suggested in the Youtube video and it works - I created a route in Google Maps, posted the link into Basecamp via the website mapstogpx.com and converted the track into a route, no apparent problems
You can also take a Google Maps route, convert to a GPX using https://www.gpsvisualizer.com/convert_input?convert_format=gpx and then import into the Connected App. I used to do this to get a route into my TomTom Rider as their own route planning was awful IMO.