Baja & Back is good. I haven't used them, but I know of many who have and I went to high school with one of the owners. I travel to Mexico on my own every winter. Last year as far south as Acapulco. You may want to check out a new forum at
Mexico RV Forum. There is a fair bit of info there on RV'ing in Mexico.
I started that forum this year, and it will take a year to get it going, but caravan info is one thing I plan on. I am also tentatively organizing a Truck Camper Caravan into mainland Mexico in spring 2011 (2-3 months). If you are interested in that email me at paul@natcoa.com. This will be through the
North American Truck Camper Owners Association , and possibly the
Lance owners of America as well. There is a thread about it on NATCOA's forum at
Mexico Caravan