Route plan with Google Map / Earth, need tech savvy help

If you are traveling in an RV, don't plan on arriving at your destination in the amount of time that google maps says it takes. The map is assuming that you don't have any traffic slowdowns, no breaks figured in there and also that you are driving the maximum speed limit allowed in all areas the entire time. We find that if we figure about 45mph average which includes breaks and gas stops, we will be fairly accurate on arrival time.