Another opinion–this time from the Colonies.
This topic came up some little time back on the Letterheads Bullboard, and not everyone agreed on what was “correct.”
I can’t address the vehicles in England or the rest of Europe for that matter—-many are not seen over here. With our domestic vans many do not have much in the way of straight, or parallel body lines. My own method is to pick what was referred to as the dominant longest line and align to it. The Ford Econoline starting with the ’91 model was the one that drove everyone over here bonkers with its ” old Coke bottle” shape. Most of us finally more-or -less agreed that the body line just below the door handle was the one to use. Using the roof drip-edge line invariably made lettering look crooked. Using more than one body line was even worse—lines of copy were not lined up to each other.
Attempting to level to a floor is risky at best; a soft tire, uneven floor, a sagging spring, uneven vehicle load — any or all can contribute to the finished job just not looking right.
FWIW from one of of us who doesn’t speak, or write, or properly spell the Queen’s English.