My son loves all things Transformers. He wanted an Optimus Prime Birthday Cake Design but NOT the robot version. He wanted a truck. I started with a very dense doctored cake mix. I made 1 13×9 and two loaf pans of the vanilla cake. I laid down the 13 x 9 as the base and then cut out for the back wheels. i stack on the sleeper cab and the front of the truck separately so I could cover the sleeper cab in blue fondant and put it on the rest of the cake that was molded in red fondant.
I used wooden skewers to hold everything into place. I added fondant details and cut the wheels out of black fondant with a round cookie cutter. The pipes on the sides are wooden skewers wrapped with fondant. I painted in the details with food coloring/vodka combo. Small silver balls added more details.
Total time about 12 hours. But WORTH it. He was so excited. Good luck!