Print your own large format pinhole camera!
The P5 is designed around a 4×5 film holder, widely available used or surplus. Film holders have a “dark slide” that protects unexposed film/paper from light, so the rubber band to close the shutter is not necessary (or desirable for long exposures). See exposure times note in instructions section.
Using the proven Pinhead shutter design, and lacking any film transport mechanism, the shutter blade is the only moving part.