Having been in Mexico a lot, though not by RV, I would suggest the Baja for your first trip if you do not speak Spanish well. The locals speak better or more English, you can't really get lost, I don't think there are any toll roads and I'm sure there are other reasons.
Here's a link to a good discussion on RV parks in Mexico from two days ago. As you go through it, you'll see several people have blogs, such as Brian & Sue on their travels in Mexico that you should look at.
Mexico RV parks.
Go back through Jim's posts, he's spent a few winters there.
Jim's BlogAlso, read this on
Mexican electricity. Bill