My dad went through something similar, though on a smaller scale. His van had a folding wheelchair lift on the back, which would block the view of the license plate from a distance but not from up close. Based on current law, this was perfectly legal, but some police officers had been trained otherwise in the past and hadn't received updated training like traffic agents had. Eventually, after he successfully contested a few tickets, the police department used a picture of his van in their training manuals -- and he put that picture in his back window, with a label for what page of the manual it was in, and stopped getting tickets.