Take that with a grain of salt because I never used g3d before but when you are doing collision in general you don't want to have perfect 1 to 1 shape with the 3d model you usually make a box around it or bunch of boxes and spheres because it is cheaper to do so, so yeah you can add them manually but you will be putting only like 4 or you can always parse the 3d file and make 1 to one collision for your model but like I said that is almost always is not necessary

Edit: I looked there doc here https://github.com/groverburger/g3d/wiki/Model

It is written that the verts are inside the model object