Aaron and his sons taking down the veil and covering the ark meant that no one except the high priest and the sons of Aaron ever caught a glimpse of the ark. The same holds true for the rest of the Most Holy things. The veil that separated the Most Holy Place from the Holy Place was unique in that it had the cherubim woven into it. (This was not the case with the veil at the entrance of the tabernacle.) This, then, was the veil that would cover the ark of the covenant.
5 When the camp is to set out, Aaron and his sons shall go in and take down the veil of the screen and cover the ark of the testimony with it.