Mexico/Central and South America - Truck Camper is best!

you need nothing BEFORE leaving USA, but if there is suspicion upon RE ENTRY, you may have your vehicle checked and the specs. will have to conform to the regulations. The EPA does not give permission to alter the original spec. The only vehicles authorized different are direct from the manufacturer and labeled 'FOR EXPORT ONLY"...These cannot be registered in the USA.

By the way, when and where do you intend to travel, and what vehicle are you talking about?