Also, for participating people, you need to put both plates, plates from your part of the world and the styrofoam Onapaffa ones, on your cars. A couple of people have been stopped by the 'Transito' police and that was the problem, only the Onapaffa ones were on. Agent Carlos verified that this is so and advises everyone to follow this procedure. What I didn't ask is which plate goes where, on the back or the front of the vehicle. Stay tuned for an answer.
Also, be sure to carry the Onapaffa information and registration papers in your vehicle. One never knows. So far, everyone has gotten away without the bribe that was being sought and without having to contact Onapaffa for back up. Cruz