This alternative chassis part is a direct replacement for the standard Duplo train and will definately be appreciated by your kids ;-)

It already has supports integrated in the model. There are quiet a few pillars underneath the bottom in inside the train's windows. I printed mine on 0.1mm layer thickness with 20% fill in Ultimaker blue (that came with the machine). Print time was approx. 30 hours so it takes a while but the result is awesome.

The roof part is a seperate piece to avoid lots of support. Glue it together after printing.

The model was designed in PTC Creo Elements Express 4.0. This program simply rocks and (more important to most private users) is free to use! Everyone should give it a try. It's more sophisticated yet not extremely more complex than Sketchup.

I really hope you like it. Enjoy!