We ahve a base for ours, and either strap it in (there are connectors in several places in the truck bed) or just depend on something holding it upright. When we take it to fill at home, the bar across the truck bed works int hat direction, and we have totes that hold things in place, My small one doesn't fit in the base, so it just rides in a tote, with something to secure it. We don't have milk crates, we have laundry baskets that act as drawer, and are used for shopping, etc., held in place between the bar and back gate