sorry my reply to this is late but i am now researching a freight hitch trip now.
this summer i worked with a girl from portugal, a total dreadlocked hippie who hitched a frieght from panama to australia. she said it was no problem, took her 2 days to find and she ate heaps for free and had her own room. she was tiny, but well cultured and said there was never a problem, she set a hammock on the dock and read in the sun. she helped cook and clean, and the men were thrilled.
im an adventurous will gadd/bear grylis type and i cant forsee a problem doing it. im looking into major ports and other travellers.
after hitching australia, she also hitched a boat to fiji, to thailand with a aman. she helped for food and sailing, but she said he was kind of creepy, but no real threat. an innocent, lonely man.
this world is tiny and our oyster, we can do whatever we want.
im planning a either a hitch to chile from canada or a hitch to the us, and out of a major port to africa.-world cup baby.
if anyone else can give me ideas, references or help with cargo hitching, id be forever in debt.