I haven't read the responses, but you can go from google maps to a track in basecamp.
Create the route in google maps, but make sure your logged in to your account. Create an account if you don't have one.
Then save it my maps(bottom left).
Go to my places and select the map you just saved.
Select the KML option, and save to you desktop or wherever.
Open in google earth and then save track as a KMZ file.
You can now import that KMZ file into basecamp as a track.
***edit, just read Dan's response. It will be nice once the KML importer works in basecamp. Save a few steps, not that I make routes or tracks from google maps.