You should be fine with the wall being legal, All ambulances, semi's, and alot of other commercial transporting vehicles all have the back glass view obstructed....I know these are all commercial style vehicles that serve more purposes besides driving them to get you from place to place, however all of these vehicles still have to abide by the same vehicle safety regulations as the rest of us (ie state inspections). Actually they have more safety regulations to pass every year, due to the fact that they are carrying precious/hazardous cargo.