Photo by Kevin Read
There are quite a few RV-specific sites where people can discuss everything related to RV'ing in Mexico.
For RV-Caravans, see the page on Caravanas de Mexico run by an old friend, Paul Beddows. They have a very worthwhile website.
The photographer of the RV pictures above also writes a most enjoyable blog. Take a look at Travels with Kevin and Ruth.
Something important to understand about RV (or any Mexico) forums is that people are reporting about their own experiences. That is often limited to one border crossing or one geographic section of Mexico that they go to every year. Just don't take what someone who crosses at Nogales and stays on the Pacific Coast as gospel for what might happen if you cross at Laredo and drive to Yucatan. Look for someone who has experience with different parts of Mexico before applying their comments to your situation.
Mexico is a vast country with man different cultures and customs. It takes years of traveling and observation to be able to make blanket statements about what "Mexico" is like. Most of us who have put in the years and the miles refrain from making blanket statements.
If you have an RV-specific site, FaceBook page or discussion board, please let me know so I can include you.