This might be better suited in tutorials:

While playing the single player campaign I am told to there is a truck spotted in the central region and to deliver it to the armory. I haven't yet found any of those things. Any suggestions?

here are the vehicle listed, so that you can get an idea about how the cargo truck looks like. http://runningwithrifles.gamepedia.com/Vehicles
If you are on Vigil Island in the campaign, the truck is most likely at the end of the northern leg of the island. It's not really "center" if you consider the island alone but it's still center of the map as a whole. This side mission is extremely hard to achieve and more for the hardcore players, or coop.

yeah do not try capping that vehicle unless you are hard core, other wise wait until you win, and instead of going to the next map go to the greys base and capture the truck... this is the only truck that can be easily captured (though only easy after you win).

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