I use a Magellan RoadMate. It works decently well for me, even though it's not an RV-specific model. While it may not always produce exactly optimal routing, it at least generally comes up with something that isn't totally crazy and sure beats guesswork with an atlas inset when in a city or town I'm not familiar with. I'm also not afraid to mute it when we disagree about how to navigate for some reason.
Any GPS system, whether standalone or a phone app, is going to be, at best, a good servant but a horrible master; it's akin to fire in that regard. The GPS is no replacement for using your common sense and powers of observation.