I invested in a B&Q toolbox (on special offer) about a year ago. It was supposed to house my Napoleonic troops but I've decided to carry my Romans and Macedonians / Greeks in it for now.
As my troops have magnetic bases, they stick to the metal toolbox really well. As the box opens up with cantilevered sides it means you can squeeze in a lot more than the 'footprint'. The toolbox takes up about as much space as two lever arch files but carries many more troops than thay can (the beauty of 10mm figures!) and is also a strong and safe alternative (the toolbox is very robust and can also be padlocked for extra security).
I've managed to fit my entire Roman and Macedonian armies in - with plenty of room to spare for extra Seleucid troops like theurophori, elephants, horse archers etc.
An elegant alternative to the box file / steel paper option (which I'll use mainly for storage when not in use).