I usually just use google maps (you can even download area's to your phone/tablet if you know you'll be in an area without cell service).
I get myself well aquainted with the route before going: Use google to route it, then use streetview for the interesting and/or tricky turns, exits, etc. (Using streetview allows you to pickout landmarks to watch for: "Oh take a turn by the big ketchup bottle", "Left at the Taco Bell", etc.) By the time I leave I pretty much know the route well enough that I don't need turn by turn directions.
If its a multiple day route I'll review the next days leg at the overnight stop (if WiFi, cell allows--the overall trip review will prepare me for whatever is at the stops).
If you really want a turn by turn device: Many people swear by the Garmin units. There is even an RV specific one that you can program your rigs dimensions in and it will guide you around roads you won't fit on.