Have a look at welding - it’s an option when you attach components. My understanding is that it takes your attached object, and adds it’s mesh data into the current rigidbody - ie, so you effectively have a single body. I’m not sure if it works if you aren’t simulating physics, but you could try having a root object as a collision object, and then attaching your new collision meshes directly to that with welding, to see if it works. I had some issues with welding in terms of bugs, but it may work for you 