Shipments of almonds, walnuts, and pistachios are being stolen in California

That shipment of nuts could be passed down in your survivalist family. First, it would be all the food you ate for the rest of your life. Then, your first child would be born and would start eating the nuts, continuously, until they died at 100 years old. They would have a child - your grandchild, and your grandchild would eat only nuts until THEY turned 100 and died (having a kid along the way.) Your grandchild's first kid would be born (your great-grandchild), start eating nuts the day they were born, have a kid, and die at 100. This final kid, your great-great-grandchild, would eat only nuts for their entire life, slowly whittling down the stockpile that lasted five generations. Eventually your great-great-grandchild would die in this basement, at the age of exactly one hundred years old like their ancestors, surrounded by the remnants of the one single truck of walnuts that their great-great-grandfather stole hundreds of years ago.

Nuts are insanely calorie dense. If you disaster-plan with a more conservative 80 year lifespan, are 30, and eat 2200 calories per day, you'll only consume about 6 metric tons of walnuts for the rest of your life. If you put that in peanut butter, which is (like walnuts) very calorie dense, you'd fit enough calories for the rest of your life into 5.5 cubic meters, roughly the size of a small bathroom.

(Not that the police officer would be likely to know the calorie density of walnuts, of course. Also, I love the pun.)

Well, it's probably carrying a village's worth of nuts...

They'd probably not look like that, but they would be different from the standard 53 foot, 8-tire, 2-axle trailer. Maybe the same box dimensions and height, but with 3 axles. Possibly double chained 20ft trailers with 2 axles each. Once you go over container shipping weight thresholds (which might be 44T like you say), you stop seeing box trucks.

The cosad trailers are amazing for their weight capacity, but typically used for heavy machinery and are designed with low floors which heavily constrains how they distribute the weight (and thus the tiered chains of 9-tire per axle bogies). There are other designs out there, but that trailer was just what I searched for because they're from my hometown and I used to be a truck driver.

Not very likely, but certainly possible. I don't see the advantage though (could exist, but I just can't think of it). I've never seen US theft enforcement and Mexico doesn't have border controls like the US, but they do have traffic stop inspections and lead-based enforcement. Any box trailer can get stopped at any time and asked for customs documents and manifests. If you stay just within the Central Valley, you'll likely never get stopped, unless you're visibly overweight. And I'm not sure the market is there in Mexico...you'd probably end up re-exporting to the US where the documentation from the origin would have the same problem (how do we make it look like we grew this instead of stole it?).

So if you went to somebodies farm in the middle of the night and loaded up a semi, you'd have to stash that semi somewhere for a month rather that selling it the next day.

For a more urban example I live in a city and there are scrappers who driver around in pickup trucks all over. It is commonly known that some will steal things made out of metal from your yard unless it's bolted down. They also steal copper wire from building sites, etc.

Now generally by the time someone notices that the scrap is missing the person has already turned in their scrap for money. And if the police figure out who did it and where they took it, the evidence has already been shredded and mixed with similar metals.

If you had to hold on to scrap for a month before you could sell it, you'd be way more likely to catch people red handed.