How do I ensure a summoned is always aligned

[VirtualSpace]

For example, if I am standing on a hill, and I summon a crate or barrel to both my left and right, how am I to ensure that the barrel doesn't stay level with the player in the z axis and appears as though levitating? I'd like my object to take into account that, when being summoned around the player, there is a ground, and the object must reach it.