Remove the lid, grill, and legs from the mini barbecue and set it in the wagon. Position the mini barbecue where you want it in the wagon.
Put on safety goggles or other eye protection. Place your hand inside the mini barbecue and hold it flat against the wagon, then drill four holes in a square pattern through both the barbecue and the wagon.
Insert screws in each of the holes, then slide nuts on the other side underneath the wagon and tighten them. It's important to tighten the fire bowl for the mobile barbecue pit so it doesn't fall out of the wagon and injure anyone when you're moving it.
Fill the area around the barbecue with decorative rocks. Use rocks with a high heat tolerance, such as lava rocks. Do not completely fill the wagon to avoid rock spillage when you are wheeling it.