Tequila: To fill in answers to your ten questions here has been my experience.
1.I never been scared to travel in Mexico. But there have been times when I was concerned.
2.We have been in RV parks along the East and the West Coasts some in the central part of the country. They were sufficiently modern to meet our needs.
3.Year before last we drove a class B RV on the Sprinter that required ULSD. I don't remember how many miles we drove in Mexico, but I do remember filling the tank with Mexican diesel 5 times with no ill effects. We had the understanding that we should keep the engine a 2000 rpm or higher to keep the exhaust system clean, which meant a lot of down shifting. That was not a problem because the Sprinter had a slap stick shifter.
4.Of all the years we have been RVing we have never stayed in the States.
5.We have never been worried about the drug cartels. We were in Mazatlan two years ago when el chapo was caught.
6.We have been traveling to Mexico since 1979. Thousands of miles with out an incident.
7.Over the years I have picked up enough Spanish that we can get by in any situation.
8.We have always gone far from the boarder.
9.Never been to Baja, but would consider it safe as the rest of Mexico.
10.Road conditions are what they are. Last year the new road from Durango to Villa Union was bad in spots. We traveled a lot on the back roads and most of them in good condition. I guess that is because there isn't much traffic.
For those who are afraid to go to Mexico I understand. I know people where we live who have never traveled more than 50 miles from home in the last 20 years or so and I would suspect that those who say they wouldn't go to Mexico don't travel much either. Mexico is different. That is why we go there.