Numbers 3:25-26

3:25 And the responsibilities of the Gershonites in the tent of meeting included the tabernacle, the tent with its covering, the curtain at the entrance of the tent of meeting, 3:26 the hangings of the courtyard, the curtain at the entrance to the courtyard that surrounded the tabernacle and the altar, and their ropes, plus all the service connected with these things.

Numbers 4:5

4:5 When it is time for the camp to journey, Aaron and his sons must come and take down the screening curtain and cover the ark of the testimony with it.