If you are crossing at Lukeville, get your FM-T and your Temporary import permit (TIP) for your rig and toad at KM 17 east of Sonoyta. If crossing at Nogales, at KM 21 south on MX 15. You need the TIP, as they are required for most of mainland Mexico south of San Carlos. They are a hologram that is put on your windshield, and for MHs and trailers are issued as 10 year permits (@ $50), and for cars and pick ups, 6 months (@ $20). You supposedly need a rabies certificate that is less than 30 days old to bring dogs back into the US, but I've not heard of anyone being checked.
When you come to a fork in the road, take it!