Commentary for Nazir 55:3

But isn't it taught that Rabbi Yosei, son of Rabbi Yehuda, says: A box that is full of utensils that one threw over a corpse in a tent is impure - as well as all the utensils inside it. Apparently he maintains that a moving tent is not called a tent, and it does not interpose at all.

And if it was placed down, it is pure - since it was placed down it is like a fixed tent, and it protects [the utensils] from the impurity, and it is not like a moving tent.