Modular Thomas the train trackmaster rail car wagons

Rail Cars for the Thomas trackmaster sets. Would probably also work with Brio if you used a different connector.
I started with http://www.thingiverse.com/thing:358779 and
http://www.thingiverse.com/thing:1620364
and heavily modified it. I had 3 goals in mind.
1. I wanted to be able to "snap" this together as much as possible straight off the printer without using any glue.
2. I wanted to avoid supports as much as possible, the only thing you should need it for is the roof of the "box car"