Dave, we haul with a grain truck and wagon. Usually, the elevator takes a sample from each. With the tongue of the wagon, sometimes the "probe which swings back and forth " can only reach the rear of truck and front of wagon, to take samples.

When combining soybeans, usually when you start, moisture is high, by later in the day, really dry.i.e. dock.13% is ideal. Start at maybe 15% end day  at 10%.  Guess where you load the wetter beans at first dump into wagon and truck. 1) back of truck 2) front of truck3) back of wagon4) front of wagon.

Corn usually, does not vary much  during day. If its too wet you wait days or weeks.Depending on the amount of drying your willing to pay. But leaving corn dry to perfection risks crop loss due to weak stalks, wind, storms, wet weather fields.Again, if you open a corn field that is 30% moisture, 15% ideal, then move to a field that has 18% corn. Where do you dump 30% corn.  Don't worry, elevator usually wins in the long run