I built this with a handsaw, about $20 worth of cheap plywood and fairing strips, wood glue and a lot of gaffers tape (to make it light tight).

Works good for drying, but if you are using a gelatin emulsion you have to make sure it sets on a level surface first, otherwise the emulsion creeps to one side, as mine is nowhere close to being level.

A quick coat of spray enamel on the inside kept the dust down. The door folds from the bottom up on a gaffer tape hinge (ghetto, but works) and has a lip that wraps around the outside of the box. To test light tightness I set taped a piece of ortho film inside and set the box in direct summer sun for 6 hours. No exposure.