Whiteboard eraser with slots for four fine-point Expo pens

This is the body of a whiteboard eraser designed to be just the right size to hold four of the smaller, more slender Expo whiteboard pens -- not those big fat ones, but the fine points (like the ones pictured).

There's a square-cornered version, as well as one with some curves. I've also included the Google SketchUp 2013 files for remixing (and here, the square one will be more useful -- I find it's much easier to remix the square one and then re-add curves than to work with the curve version).