Appreciate this thread is old but have dug out my old 310xt for a trail race. Anyhow its a little simpler now. Use Garmin Connect. Select training and then courses. This will allow you to import a gpx file or tcx direct into connect. It then wants to know if it can use openstreet map, the type of route and then give it a name. Then you can select to transfer to device. This will open garmin express and assuming the 310 xt is connected (via ant) it will push the course direct to the watch.
Appreciate this thread is old but have dug out my old 310xt for a trail race. Anyhow its a little simpler now. Use Garmin Connect. Select training and then courses. This will allow you to import a gpx file or tcx direct into connect. It then wants to know if it can use openstreet map, the type of route and then give it a name. Then you can select to transfer to device. This will open garmin express and assuming the 310 xt is connected (via ant) it will push the course direct to the watch.
Adding incase anyone else digs out an old 310xt.