Something more than a "locked truck trailer" I suspect.
Not really. The trailer needs to be located far enough away from other structures, and needs to get the okay from the local fire marshal. The caps need to be in a heavy-duty, thick steel box with locks. The locks are covered so a bolt cutter won’t cut them, but a cutting torch would get the box open.
The “dynamite” needs to be in a separate locked trailer. I’m guessing it isn’t the stick dynamite found in Bug’s Bunny cartoons, but probably a binary component where you mix them together (basically fertilizer and jet fuel). But still makes a big boom.
I would be more concerned the blasting caps were stored in the same container as the “dynamite”.
When I was a lad, my father would take me with to the quarry where he was a blaster. Caps and explosives were ALWAYS stored separately until ready for use.
I say INSIDE JOB!