The "problem" with the limited access to PC install versions of topo maps is in my experience not a big problem. I never use topo maps for navigating routes since that rarely works well, paths do not connecting to each other or to roads makes navigating erroneous. usually I set waypoints at strategic places and use the gps as "moving map" to find my way.
Then you can reverse engineere the img with gmaptool and get a pc install from which you can select the tiles needed to be transferred to the gps. This is a workaround for old gps models with limited memory.