There is many ways of achieving this. Not sure how your models looks and what is your setup.
The simples way would be to create StaticBody and put into it
couple CollisionShape nodes thanks to which you can define simple shapes
like spheres and boxes to create collisions.
More complicated but giving better control way would be to model
simplified collision mesh in Blender. To do this just model your
simplified mesh and add it to your “visual” mesh with a name
suffix(postfix): -colony
If you want to model your collision mesh in Blender and you have any problems, then you can check this vid: https://www.youtube.com/watch?v=llYeyuVTFR4&feature=youtu.be It was not made strictly for learning purposes, but you can see what’s the setup exactly in this movie.
kubecz3k | 2016-04-11 08:06
How to upload from Blender CollisionShape for RigidBody?