I have tested several packs of cheap printer paper and found it to have a neutral pH, so although I wouldn’t put it inside a box it should be fine outside. Polypropylene label holders are good as you can change the contents. For a cheaper method we have used printed labels pasted onto the box with a water-soluble adhesive or even a neutral pH PVA adhesive. The labels include boes which can be ticked when condition checks have been carried out etc, which is easier to do when you don’t have to remove the label from the holder.
