France and I carry a piece of red and black cotton cloth sewn together along one end. There is a tab sewn on either side to affix a string around the back of the darkroom to prevent pulling out. This, along with a sheet of red glass is packed with our supplies when we travel. When we arrive at a location we find a cardboard box that fits in our rental car, tape it shut and then cut an opening from one of the long sides.
The extra piece is then cut and fitted to the inside of the box to act as a divider between the silver and developer sections. The bottom is lined with sheet plastic up to about two inches on the wall in case of spilling the silver bath.
The cloth and red filter window is attached with duct tape and we're ready to go.These can be used in the car, on cheap saw horses with elastic cords or on the ground. After the shoot, we remove the cloth and window and throw out the box. Have made plates all over the world with this system and the fastest we've been clocked putting one together is around 15 minutes. If I knew how to insert a picture here ...I would. Help. :-) contact me directly for a picture firstname.lastname@example.org