Very strange !
A gmap folder is only for use on your PC/Mac and can not be seen on your gps. PC/Basecamp does see your gmap and with Mapinstall you can install the map on your gps.
For Basecamp: depends of your operations system (Windows XP, Vista, 7 ..., or Mac) where to put the gmap folder.
Or you put the map on your gps and want to see the map from your gps in Basecamp ? Then its a question of the Mapsource-flag I assume. But that is not neccessary when you have the map as a gmap folder on your PC/Mac.
So, I can not quite see what you exactly meant.