Interesting that you say that. For my car EVtripplanner underestimates RM required for a trip pretty consistently but the car's nav system is usually pretty close unless weather is an issue. I get a general idea of the route, miles and elevation change from EVtripplanner before a trip for each leg (and print them out, including elevation plots [GPSvisualizer.com], to keep in a reference notebook) and then just let the car nav and energy plot guide my driving to each Supercharger stop. I then log the expected (from EVtripplaner) and actual RM used on a spreadsheet, for future reference when doing the same route again.
As routes become familiar just setting nav, charging to a comfortable buffer, and driving the energy plot is pretty straightforward. EVtripplanner helps with mapping out new routes and identifying potentially difficult legs of the trip.