BaseCamp or RoadTrip will not open gpx files when you double click them.
You must use File > Import.....
I exported files from BaseCamp to a folder on my desk top. When I open that folder it opens in Textedit and is pretty much read only code. It doesn't seem to matter where I export it, it will still open in textedit. What is the best application to use to open the .GPX file?
Why do you want to open it in an app. other than BaseCamp or RoadTrip? If clicking the file doesn't launch one of these, you need to change your file association.