In regards to post #3, I have some folders I made with that same tutorial. They're actually a good bit wider than the plastic folders you see on the cart in the picture, so they wouldn't save me any space. (I got those folders at Goodwill, and I don't remember the name on them, but they're the same size at the JetMax folders, only they're plastic.)
Also, once I put in the row of 12x12" hanging folders, there isn't room for a 2nd row of 12x12" at the top. Does that make sense?
Anyway, for some reason, I didn't get any updates to the thread, and my husband and I did something else instead.
I asked him what he thought, and he said that the whole bottom "shelf" can come off. (He's the one that put it together.) He took it off, and now I have room on the bottom for another row of hanging 12x12" file folders. They "overlap" the top folders by a very slight margin, but it's a workable solution since it costs me nothing and accomplishes what I set out to do.
If my cart happens to collapse, I'll be sure to post an update so you know!
Seriously, though, it has several built-in supports to keep its shape, and my husband didn't think this would create too much strain. I don't wheel it around at all; I just keep it stationary.
I'm attaching a picture of the finished product, since they're always worth a thousand words. Thanks for your help!