In Basecamp go to the file menu and select "Import into.." to select you GPX file having saved from the email to somewhere on your hard drive.
When you have the route in Basecamp you can then either drag it to your plugged in device or select "Export" from the file menu and place it in the /Garmin/GPX/ folder on the internal memory of your Zumo (assuming that it works in a similar way to the 660). Your Zumo should detect the presence of the new data the next time you start it and offer to import the route.
HTH