There is one more option, although not quite as adventurous. You can put your vehicle on a ship in Houston and pick it up in Cortez, Honduras. You would miss the boating in Mexico, but this time of year ain't all that great for the northern runs around Santa Maria- they will pretty much be dewatered (except for the Salto) because we're going into the dry season.
The runs around Veracruz could be flowing, which might make it worth looking into putting your vehicle on a ship out of Veracruz. Make sure you check out the Alseseca. I have no information as to whether that shipping service is available, so you'd have to check that out.
Driving in the Northern part of Mexico is pretty secure after you get past the border, and the furthest south I've driving is Veracruz, so I can't give any personal account about what it's like to make the Big Drive. However, even though I've driven to Mexico on boating trips six times, I don't think I'd make the trip through Chiapas. Some friends of mine did it in '94 and had no permanent trauma, but you never can tell. Maybe I'm getting old.
Information I found: