I was one of the judges at Chattanooga. With 3112 entries, it required some serious work to pick the top entries.
For dioramas, don't try to put EVERYTHING into a scene. Less is better. Consider how the main subject got into position; tanks, airplanes, and artillery are not weightless and need to be moved.
Remember, gravity is a heartless master, this on a ramp or slope roll down hill.
Dak