We present the design and construction of a custom neutron-transparent sample environment for in situ moisture-dependent neutron dark-field imaging (NDFI) experiments for the imaging facilities at the Paul Scherrer Institute (PSI), Villigen, Switzerland. This simple setup, combined with a moisture generator, features a continuous flow system to ensure a constant homogeneous flow of humid air to manipulate the sample's moisture conditions at room temperature. To facilitate neutron dark-field imaging measurements, the chamber has a slim design to maximize the sample-detector distance scanning range. The chamber can maintain static or dynamic relative humidity conditions, allowing for humidity cycles. Beyond moisture-dependent studies, the system's versatility allows its utilization in any type of gas stream-dependent study. This technical note details the engineering considerations, construction process, and validation of this sample environment.