Most RVers travel Mexico from November to April or so. Some do it to avoid the hurricane season, but most because that's when the weather is so much better than farther north. We do our Mexico travel in the winter too, and that means that we don't get to see what the campgrounds are like in the summer. We do know, however, that many are not open, despite what they tell us in the winter.
Cheri and Ray Wise recently completed a summer trip (summer 2007) and were kind enought to provide a spreadsheet showing where they stayed and what they found.
Click here for a PDF(Adobe Acrobat) file of the spreadsheet.