In the movie RV, at the beggining, the daughter notes fuel mileage. She makes a comment about diesel fuel, the correct fuel for a vehicle this size as RV have diesel engines because diesel engines provide more power. However, when Robin Williams is fueling the RV, you can clearly see that he is using Unleaded Gasoline which is not approved for diesel engines.

Also, when they first start there trip, Robin Williams grinds the gears of the RV's transmission. This is impossible as the RV has an automatic transmission & it is impossible to grind gears in them.