I don't know that there necessarily WOULD have to be anything in the mausoleum, if only one person is allowed to see it. It's certainly possible that they've made a mock-up of the Ark, though. I wouldn't think it would be all that hard for a craftsman who knew what he was doing. I guess if the story about Solomon's son stealing the Ark is correct, though, then it's the later Jews who had the fake Ark. Then again, who knows how many Arks there might have been over the years?