There is another easy way to convert your file. Save your Google Earth file in .kml format. Download "Ride Leader" by Trailtech. It is free and will open gpx and kml files. It will also allow you to do any needed editing. Additionally, it will also edit Track segments. Open your Google Earth file (kml) using Ride Leader. Once you open the file, save it as a gpx file. Take that file and load it to a memory card using HumminbirdPC. You can then upload that file to your Humminbird unit. Going from Google Earth to Humminbird format takes about minute. I like GPS Babel but it will only convert files and not allow you to perform any editing.
Have a Blessed Day,