Nogales is a piece of cake. They even have a sort of Ombudsman that will help you if something is amiss with your papers. I have never seen an Ag inspector. If they have one he or she is asleep somewhere. Back in October I was in the line to pay the Magdalena toll when a Gringo lady( actually she was Canadian) knocked on my window. She wanted to know where she goes to get her FMM!!! I told them to turn around!! I have run into others in Kino that came all this way with no papers. They could have had a pet Gorilla with no problem!
Moisheh