I'd recommend a set of street tires for the run down, swapping to say Pirelli MT21's at a dealer near the border, get him to hold them for you, then swap back on the return. A few thousand off road in Mexico on knobbies or near knobbies and they'll be about done. Cheaper in the long run.
Try and do the round trip on anything but a pure street tire, and you'll have slicks by the time you get back, and half or more worn out in Mexico, so not much fun there.
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Grant Johnson
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www.HorizonsUnlimited.com