When I crossed the border from US to Mexico in a UK registered red camper van, there was no border from US to Mexico. I was meant to hand in some documents to s

When I crossed the border from US to Mexico in a UK registered red camper van, there was no border from US to Mexico. I was meant to hand in some documents to show the van and family had left the US but we managed to get into Mexico without seeing any US customs / border. Speaking to the Mexican side they said the US border controls was about 2 miles back up the road so we didn't bother and just carried on South. So probably a bit of room for some searches on the US side