I have not made the trip myself ,so can't offer any first hand information,however we do come across a rig or two who are mostly from Europe that are either heading to or returning from South America that stop in Mexico.
They are usually German or Swiss although presently there is a Couple in Our RV Park who are Australian/Canadians who are intending to take their 34 foot Class A Motorhome all the way to Patagonia.
The Internet is not cooperating Today ,so I will ask Them where they obtain their information and get back to You.I will also ask them to contact You via a PM !