And below I think is exactly what you want.
I've tranformed some of my tracks (.gpx) to a transparent map file (.img) using [Only registered and activated users can see links. ] and created a new mapset using a solid greek Topo Map and my transparent map of tracks.
The red and black color of tracks is due to the custom TYP file I've added to the transparent map.

Mapsource:

con03


Basecamp:

con04c