We use Garmin and build the routes in Mapsource first then upload to the Nuvi's.
The newer Nuvi's build the route in Mapsource then import to Base Camp for the upload. Base Camp doesn't work well for building routes. Also tends to overwrite waypoints with the ones in the GPS.
Mapsource does a better job of letting you view sections of the route in Google Earth such as intersections.
Paper maps as back up; we carry a box of them.