Rick,
There are different rules for different parts of Mexico. The rules for Mainland Mexico differ from Baja (where we go all of the time). Briefly, here is a quick-n-dirty "laundry list:
1. You will need insurance on both vehicles. No matter what your insurance company says, the law in Mexico states that insurance MUST be issued by a Mexican licensed Insurance company. I would suggest getting the "legal" suppliament on the policy...just in case....! Remember, in Mexico you must prove your innocence; not the other party proving your guilt.
2. If either of your vehicles is not title-free, you must have a notorized letter from the lienholders indicating its OK to take your vehicle(s)into Mexico. The letter must contain the year, make, model, VIN and the dates of your travel. We usually get our for a 1 year period as the banker is a personal friend of ours and we go down to Baja very frequently.
3. There are "border regions" (the Mexican States that border the US and are within 75 miles of the US border)that do not require a "Vistor's Visa". You must obtain a Vistor's Visa (a) if you plan on travelling more than 75 miles into Mexico and (b) if your stay or time in Mexico is longer than 72 hours. These are good for 6 months (make sure you specify 6 months or the folks sometimes issue the document just for the duration of your stay. These cost about 20 bucks each.
4. If you are taking pets, make sure you have the rabies vaccination papers with you---mainly to get BACK into the States.
5. No firearms, ammunition,or explosives of any kind. If you get caught, you will become the guest of the Mexican Government for an unspecified amount of time...!
6. I think there is a limit on the amount of alcohol & tobacco products you can take into Mexico---but I'm not sure of the quantities.
7. US Customs treats US citizens like they are not US citizens at times---guess it depends on the "Alert" status. Had some pretty nasty US Customs officers give me a bad time---got even (I guess) through my Congressman....!
8. here is real good website that can answer most if not all of your questions:
http://www.instant-mex-auto-insur.com/
9. We love Baja and made some really good friends down there. I guess its the same anywhere you go---treat others with respect and honesty and you'll be OK. The fishing is great on the Sea of Cortez and there is so much stuff to see & do.
10. Here is some info on san Felipe---neat place:
http://www.bajaquest.com/sanfelipe/baja13b.htm