In Missouri trucks licensed for over 12,000lbs are issued only 1 plate and that is required to be displayed on the front of the truck.
If you need an extra plate, for a fee they will issue a paper plate to display on your window. I don't know how that would relate to a truck.
When I lived in Ca I had a short bed truck with an 8ft camper and pulled a horse trailer behind it for thousands of miles in ca and Arizona. During that time I did get pulled over a couple of times for speeding and even received a citation and another time a warning, both were deserved, but nothing was ever said about the license plate.
And yes the Leos are out there doing a great service for us.