There are a total of 6 Explosive Barrels they will be a red barrel, but with a flame on them. Fair warning when burning one of these, it will light your starter on fire and you will have to repair your device that burns the fuel.
1-Will be at the farm shortly after getting repair tool.
2-It will be after getting passed the large windmill
3-You will be stuck and have to hook your front latch to a post, the barrel will be right behind the post.
4-Shortly after you receive your new tires.
5-At a railroad track once there is light snow on the ground.
6-Shortly after you get off the big 4 legged metal thing, it will be in the open.