This tip describes the construction and use of Tyvek tubes filled with activated regular density silica gel desiccant to maintain low relative humidity conditions within storage cases. Measuring 2 x 24 in., they are used to help achieve an in-case relative humidity of 15% or less for collections of unstable archaeological iron artifacts. The tubes are constructed of sheets of needle-punched Tyvek (Type 1622E) formed into tubes sealed with Tyvek tape. Custom-cut bag clasps allow resealable access through one end of the tube for refilling with reconditioned silica gel. Tyvek straps are attached to each end of the tubes to secure them to the sidewalls of the case in areas that will not interfere with access to the stored collections.