Whiteboard Tray, modular, parametric

I recently bought a whiteboard to help me keep track of how little actual work I'm getting done, and how much time I've recently been burning up making things to post here. It came with a tray that will barely hold five skinny pens and an eraser, and it has no sides making it easy to knock things off. So I've burned up a bunch more time making a modular tray system that expands to the whiteboard's width.

This tray will work with any whiteboard that has a frame made of a channel material which will accept a T shaped rail. It will not work with frames that do not have this channel (e.g., solid wood frame). This is the whiteboard I bought and used for the default sizing: http://www.amazon.com/Master-Boards%C2%AE-Drywipe-Magnetic-Whiteboard/dp/B00TQV2X8G

Note: The defaults in Customizer and the STLs I've included are optimized for a Lulzbot Mini which has a 0.5mm nozzle and uses 3mm filament. If your nozzle is not as wide, or you wish to use cut sections of 1.75mm filament to make pins, you will need to make adjustments in Customizer to ensure proper fitment.

Assembly is simple -- just slide in the correct end-piece, then all of the intermediate tray sections, then the other end-piece. Each piece is held together by pins, up to three per side though it may not be necessary to fill all the pin holes.

The only potentially confusing parameters involve the T rail. Use this image as a reference for making adjustments to the T rail: