Since you are traveling across country in a rig that is about the same height as most commercial truck tractor/trailers, ask yourself how many of them have their I-phones wedged up on the dash using them for navigation.....I suspect none of them do.
If you want to make sure you are traveling safely on the correct roads for your height, weight, and other specifications you need 3 things:
1) RV or Truck GPS
2) Current Trucker's Atlas
3) Pay attention to each and every sign while driving.