I was having the same issues, I live in AZ. The standard plates that come from DMV only have one, in AZ you only have to run one plate in the rear of the vehicle.
However if you order Vanity Plates, you get two from DMV, it's an extra $25 a year for the Vanity Plates. I mounted the second Vanity plate on the back of the camper, and then went down to DMV and told them I lost my registration sticker, they issued a duplicate, at no charge and I attached it to my vanity plate on the back of the camper. I now don't have to remove the truck plate each time I load the camper. I have a large 1121 Lance so the truck plate in the rear is concealed.
No matter, everything is legal and checks out when they run the plates. At least in AZ it's an easy fix.
Rob
