anytime you put a container in a position where a potential impact can occur. impact points are calculated by many insurance companies to determine anything from cost to risk to repair. putting a can of explosive fuel at an impact point (rear of vehicle) increases risk and potential costs to insurance companies. carrying a lower profile container on top of the vehicle reduces the chance of impact by the numbers and to sources such as low bridges or parking garages. with most SUV's the height of the increase would not be significant enough to elevate the chance of hitting an overhead crossing. (car washes city garages) would be the highest risk,,,,,,,,course if you have added fuel the last place you would be would be in a city garage..........clear as mud?
by the way. nice plane.