No options to import custom collision shape into the root node

I have posted this issue on every place that I know in order to find an answer with no luck.
The problem is about custom collision shapes, I made a car and I made a collision shape for it, but when importing it in Godot, using the -colonly command (EDIT: I have found the official mentions about the commands, I am really sorry, but still that doesn't solve the issue) it creates a separate node for the collision shape that canot be accesed by the root(VehicleBody) node, so it asks me to give it another collision shape in order to work.
This is my Blender project setup:

I could't find any informations on how to solve this on the web and in the documentation.
Also Blender cannot export .res, .tres and .shape files so I cannot add it that way either, and there are no mentions on how we can actually make those type of files on the web or in the docs.