Some box deterioration is due to the use of acidic paper which will often decay overtime and just fall apart. I am told that most paper from the middle of the 20th century back is at least slightly acid. There is a spray on chemical that can be bought at Library supply stores that will prevent this deterioration. I have bought it in the past and used it on some boxes that were falling apart with some success. Over the past decade I seem to be having less of a problem, but probably because my collection, including boxes is stored in air conditioned areas.It has been a number of years since I have bought a can of this so can’t give you any hints.
Today there may be much better alternatives available. You may want to check with a local liberary, particularly a university library or one that maintains old paper items that must be protected.