Hi Jeff and Matt,

 Let me just make some comments on what Matt was saying.  More than
just a flight plan, since recently, anytime you cross the US border
you have to file an eAPIS (https://eapis.cbp.dhs.gov/), going out and
coming in, Mexico is no exception.  In my experience flying in Mexico,
the towered airport to towered airport thing doesn't hold true.  Just
file to your destination, but you do have to stop at an international
border airport to pass immigration and customs.  Double check you are
insured and that your insurance complies with Mexico's requirements,
most do.  Rick Gardner of Caribbean Sky Tours
http://www.caribbeanskytours.com/ is the expert on all this stuff.
Even though their name is Caribbean, they know all of Mexico.  Contact
them, buy their guide and ask him about the details.  One thing that
may be needed in is a letter of authorization from the DGAC, Mexico's
CAA,  to fly your experimental aircraft in Mexico.  Rick should know
the status of this, some people get asked for it some people don't,
but I believe it is still officially a requirement.
Anyway, based on Jeff's post, he may already know all this stuff, but
I thought it worth mentioning some of these newer details for others
who are reading.

Jeff, as for a recommended route, I have no idea, but again, you might
consult with Rick.

Tim