You could build a Gmaptool Mapsource version but you'd loose search, not a good option.
Better to download the original gmap folder on forum and have it fully functional in Mapsource and in Basecamp.

Must just have a patched version of both the programs and put the gmap folder in the right path, all the needed infos here:

[Only registered and activated users can see links. ]
read :
Have you downloaded a Mapsource map version?
and
Have you downloaded a Mapsource Gmap folder ?


or you have this option too
[Only registered and activated users can see links. ]
it will be faster in Basecamp than having the img in any sd or garmin device