Lid for SD Card Rack

I like AndrewZorn's minimalist [SD Card Rack](http://www.thingiverse.com/thing:64847), however it is not suitable to transport a bunch of SD cards because they are just loosely inserted in the holder. I tried modifying it such that the cards would fit with just enough friction that they would not fall out, but this proved a hassle and I'm sure that the plastic would deform over time and the cards would either fall out anyway, or I would need pliers to get them out.
Therefore I went for a simple