First, let me say, I am sorry we missed meeting some of you last week.
However, in response to the original question. We went down to Monterrey, Mexico from Laredo, TX last Feb for some medical stuff. Way cheaper and great quality of care compared to US.
We didn't take the truck and trailer, actually took a bus so we could scope it out for future trailer travel. The toll road was in excellent condition, we wouldn't hestitate to take the trailer next time. We felt very safe the entire time, spent about a week and relied on our small amount of Spanish, a dictionary and public transit/taxi. No major problems.
That being said, we have talked to a lot of people that suggested always travelling in a group, so that someone can stay with the rigs at all times. I suspect it is no different than US, some places safe, some not.
We have seriously considered spending a winter down there too. Would love to do some more diving. Maybe there could be a NuRvers caravan sometime in the future?
Jenn