I don't think Drivesmart has Tracking or the ability to upload other tracks/maps/routes.
Depending on the Smart Phone. Might try turning off Cell Data, so that it does not use Cell Tower Triangulation, but instead uses the built in GPS. Might take 10 or 15 minutes to find satellites but once it does, it should work without Cell coverage.
New Garmin. I really like the looks of the GPSMAP 276Cx, however the $$$$. I use a Garmin Montana. Works for me, but although at the time I bought it, it was a large screen, it's really not that large. Maybe if you could find a used Montana, it might make sense.