Just going left and right I was able to create a tall stack of cargo loading beneath the previous selection.
UPDATE- Maybe not. I tried recreating and it works as intended up in the air above nothing and on a cargo loading platform. It might have been because I had initially placed the ZonePropertyManualLoading on top of the caravan model (maybe collision issue?) or because it was inside a reference (which might be a problem). I'll try to test more later.