I got many of the ideas behind this from this website! But put them together my way.
For my son’s Camo Tank Birthday Cake I used a massive 15 x 12 x 3 cake pan and for the top I used an over sized bread pan (3″ deep). I think the key is the size, so the Hershey bar treads look to scale. The top layer was supported with wooden dowels and a cardboard divider.
The rest is all icing. I iced a 2″ perimeter along the bottom sides with dark chocolate (where the treads will be). On top of it placed Hershey bar pieces for treads and Oreos on the sides for tires. The Oreos didn’t need support but I may have used a few toothpicks here and there.
Then use a different icing for the body. I actually put 2 containers of prepared icing in a bowl and dropped some green food coloring on one side and some brown on the other, and mixed only a little bit. It formed sort of a natural “camo” look when applied.
Still, because a lot of white is showing, I finished off the white parts using green and cold icing spray that I got at Walmart very cheap. For the soldier, I just dug out a small hole and put an Oreo standing up prior to icing. I used toothpicks as supports.
A few decorations and you are good to go!