My pharmacist puts three of those tubular moisture absorbers in my mestinon. I've never had any problems with them crumbling.

But I will be changing my location of storage after reading this thread. For the last few days, I've been keeping all of my vitamins in this big basket that I keep by the window (it's -15 right now). I was putting my mestinon in there too. There's also a heater under the window, so sorta a really bad place to keep it...lol