When I’m trip planning at home I just use Google maps to get a good idea of the route. On the road, I use a Garmin 795. An RV GPS, and especially Google Maps, are not perfect. But an RV GPS is invaluable when it comes to RV-specific features like avoiding low clearances, steep grades, and more.
I also carry a Rand McNally Motor Carriers Road Atlas, but I hope i never have to break it out…lol