An apparatus for forming a container is provided. The apparatus may include a blank that includes: a first support panel defining a first height; a second support panel; a first bridge panel connected between the first support panel and the second support panel, the first bridge panel defining a second height; and a second bridge panel connected between the first support panel and the second support panel. The apparatus may further include a flexible sheet extending from a first end to a second end, defining a sheet length, and configured to form a first concavity. In some embodiments, the sheet length may exceed lengths defined by the first and second bridge panels. Alternately or additionally, the first height of the first support panel may be less than the second height of the first bridge panel.