This is one of the best episodes IMO.
The buildup toward exploring the giant spacecraft was incredible. It's too bad it's not real because it's a pretty crazy story. Loved it.
The mannequin of the alien, in the end, really closes the case. There's no doubt the entire thing is a hoax.
Although... Of all places, would the moon be a great place to look for traces of aliens? Its surface is way older than Earth's because it doesn't have tectonic activity. A spaceship parked somewhere might be hidden under a couple of inches or feet of lunar dust, and have its surface dented and damaged because of asteroids... But it would still be there in theory, even after a million years. No rust, no erosion.
While on Earth, I don't think a crashed UFO would survive the elements for a million years. Let alone a volcano or the ocean's bottom.