Toolmaan

Just took delivery of my 2021 Silverado 2500 last week. Liking the truck so far. I am wanting to add a tool box to the bed. Prefer under the rail mount to the floor of the bed but really don't want to drill holes in my new truck. Anyone have a box back there? This truck is a Sport Z71 LT crew with the factory spray in liner. I may go with a rail mount box if need be.