Well, you cannot craft large backpacks or diving tanks, so it isn't crafting. It seems that these get assigned to the person that loots them and then are locked to them. If they drop the empty backpack or the diving tank on the ground, other players get a "you cannot loot this item" error message.
I know it is tricky, because you don't want large backpacks to be lootable when they are on the player or when they are dropped due to death, but you do want them to be lootable and able to be picked up when the player throws them on the ground voluntarily. Just not sure if that is possible to distinguish.