I use Maptech Chart Navigator/Pro in my PC to create my route. Then I transfer the route file to my laptop. Finally I connect my laptop directly into the Garmin in my boat, via an interconnect cable, and either send new routes to my Garmin, or capture actual track information from my last trip.
The chart I created showing a safe route around the Johnson Shoals, for the South Seas fun run, was from Maptech Chart Nav/Pro.
Maptech Chart Nav Pro, list price $499
Maptech Chart Nav, list price $249
Interconnect data cable for Garmin $39-$79, debsnding in Garmin model.
I attached a screen shot, you should be very familar with the location.