Chris,
Sounds like a very interesting trip. We have contemplated a driving trip to SA as well. Still a couple of years off-- elderly parents.
Agree a trailer would not be ideal, both from container size as well as suspension issues on miles of less than ideal road surfaces.
Diesel has been recommended as the preferred fuel-- cab over,Class C or I guess a very short A. Have to be able to run on the "regular"/high sulfur diesel, no nothing in the U.S. of recent vintage.
If you get specifics on exactly the max dimensions/ size-price breaks for the Panama to Colombia ferry, would appreciate it-- have received conflicting information.