In my mod, this unit is the lonely that will be found a new colony.
Why? Because, it was stupid (for dazio and I) that a criminal who walks in the territory could found a colony.
http://www.dawnofanewera.fr/images/ScreenShots/BuilderWaggon001.jpg
How to have a new builder wagon?
You can buy it in Europe but its price will increase.
You can build it in one of your colonies too.