Requested via note. This is the method I use. Not everyone is this thorough, but I firmly maintain that everyone should be. This will work for regular props as well, just disregard the part about putting them in the character's hand.
I will refer to Genesis, but this will work with any figure in DS4.5 Pro. Gen 4 and 5 have the same bone names so smartprops for them are interchangeable for the most part.
First, in your modeler:
Model your item flat on the ground. Yes, I said flat on the ground, not in the hand. If you've already modeled it in the hand, move it back to the ground and redo the object center. Trust me, you'll thank me later. Export it flat like this. Name the obj ItemNameCTR or ItemNameCenter.
Second, in DS4.5:
Import your new mesh.
Load an UberEnvironment light and render it from different angles to make sure the normals are correct. If they are correct it will render white. If it renders black