France [Scully] and I have probably made upwards of a dozen portable darkrooms, since we make on site as needed. Many of these were made during trips overseas and were discarded at the end of a shoot. We bring a large cloth made with a layer of thin black black cotton sewn on one edge to a layer of red cotton. Any light that gets through the black is filtered with the red. We also take a pane of deep red stained glass for the safe window.
At the location we find the largest cardboard box we can find [usually behind an appliance store] that fits the back of a rental car or van and purchase a roll of duct tape and a box cutter. We tape the box shut and then cut a portion from the front and a little from the top. With the extra cardboard pieces we fashion a divider on the bottom of the box to establish the silver bath and the developing work areas. Then we cover the whole bottom with plastic, taped up at least 3" up along the sides for spill protection. If we don't have sheet of plastic, we simply cover the whole bottom with overlapping duct tape. Then we cut a window for the red safe window and tape that in place. The cloth cover is taped over the opening. After the shoot, we reclaim the cloth and window and throw the box away.
