There are quite a few RV-specific sites where people can discuss everything related to RV'ing in Mexico. My favorite is run by an old friend, Paul Beddows at Mexico RV Forums. The advice here is quite helpful and dependable.
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.