My guess is that someone is storing stuff that they would like to keep out of the prying eyes of whoever
I would rule out moonshiners based on the fact that to make moonshine, you need heat. I don't see any chimneys or even a stockpile of wood for the fire. Another strike against moonshiners is that such stills are usually outdoors because of the heat.
An interesting feature of the building with the steel door is how high the door is with no steps or ladder. This leads me to believe that whatever is in these buildings, it comes and goes in the bed of a pickup truck.
My uncle kept his stock of dynamite in similar structures, but there was a drivable trail to get to them.
MANY years ago, a couple of teenagers took some shots at a similar building near Des Moines that contained about 12 tons of dynamite. It didn't end well for them. https://www.upi.co...gns/6735438238800/