If we're trying to ban ways to store loot quickly, let's get rid of chests inside rooms, because you can easily throw things in them.
But really, I think this would be one of the worst rules (besides grief-bait) because they aren't just for storing loot, they are to get people to also fall in, a defensive system. My batcave has had many people that aren't me fall in, which earns me loot.