I was at a coin show today and spent my time finding an inexpensive coin storage box that would fit the 3D World slide mounts. I settled on this box:

http://www.wizardcoinsupply.com/product/quarter-tube-storage-box-blue.html

The price is right. It holds two rows of slides without too much free space. 36 on each side for a total of 72. You could probably fit a bit more if you wanted things to be really tight. The cardboard inserts are easily removed. I changed their configuration to make two rows and four compartments within each row.

Just passing along the info. I'm glad I finally found a storage box that works! No more ziploc baggies everywhere!