This is a similar solution to what my predecessor here at NYU proposed. They utilized reused and re-purposed acid-free folders to serve as spacers in archival boxes. For the short-term, they have mostly held up, but as I am re-surveying parts of the collections, the rolled folders often haven't held up to the shifting weight of partially filled record storage boxes or document boxes.

I've made a big push to replace the adhoc spacers with corrugated board ones from Conservation Resources. Of course, we also the advantage here of very standardized box sizes, so bulk ordering spacers made a lot of sense.