The only thing sitting is the box does is allow the destructive process to continue unobserved. Zinc pest is inherent to the composition of the zinc alloy. High Lead content (we are talking ppm levels) is by far and away the primary culprit. It's in there, you cannot remove it, and you cannot stop the process. That said, certain conditions seem to accelerate the process. Some castings go for years before the damage is evident. Some show in only a year or less. I suspect the higher the lead contamination, the faster the process.
I've had a K-Line coupler and truck assembly disintegrate on the layout. The car was fine for one operating session. The next time I coupled it up, things did not go so well. I've learned to inspect castings for signs of zinc pest. I pull the offender out of service and go looking for replacement parts. Sometimes I get lucky, sometimes not.