I've really only seen one out of the back of a car. My friend and I were exiting a gun shop, and this mexican guy approaches us asking if we wanted a carne asade(sp?) burrito, or something along those lines. My friend knew what he had, and said they were really good, so I figured why not help a guy out, especially since he was pulling at your strings with the wife and baby. Can't remember if he actually had the stuff in his trunk or back seat, but it was all fresh and in sterile containers, and was really good!
Most the time they have a food service van that they peddle them out of. Never tried them either, but they'll usually park near a big lumber yard or something like that, and if you roll by around lunch there're usually several people buying food.
