Yes, Dee - they DO have their own rules. Additionally, you would need to have "Mexican Insurance" to drive into Mexico, which is not horribly expensive, but I don't really know how well it works, since we never had to file a claim.
Then, you go through the rigamarole of stopping inside the border on your way down to register your vehicles so they can be sure you are not going to be selling them or buying new ones while in Mexico. Coming back, you have to do the reverse process inside their border. There were no instructions to do this, and if we had not been with a couple that makes regular trips, we would not have known how to find the place or to do it at all. I have no idea what happens if you don't make these stops (which took a bit of time) and try to return to the States without the proper paperwork.
The busses in Mexico work better than the ones in the US, in my opinion. But, they can be crowded, old, dirty and you have to be wary of pickpockets. Carry your money, credit cards, passports, etc. inside your clothing. A friend of ours had his front mounted fanny pack opened on a bus and his wallet was taken on a trip we took from Guadalajara south to Ajijic. Other than that, we had a great time!
- Jack