OK, enough of the non-advice already - other than Jon V. Here's a good blog with lots of campsite co-ordinates: SongOfTheRoad.Com - sorry no clicky. And, look up ExpeditionPortal.Com and check under the "Forums" section for "Adventures In Progress". Lots more travelers doing your thing under that site than on this site. Also, check with the Mike & Terry Church guide "Camping In Mexico", - if you wait at the border or on the first few stops into the Baja you may run into a number of Overlanders heading to the same destination. Lastly, if you spend a few nights at the OverlanderOasis.com just south of Oaxaca, you are sure to run into people heading south. Personal Message me (PM) if you need. Tallman.
