Just a few quick ideas. If the camera is going to be large enough for you to fit inside (?), you could build a flexible tunnel (from textile, for example) with two light tight lids and take the paper with you in rolls, that you can tape then to the wall of the box inside.

I'm not sure if the material is important with large pinholes where it's easy to make a round whole in the plate with more pedestrian methods. I'd personally go with black painted brass or bronze.