Collision Colliders - Box or Mesh for Terrain

So, I’m currently grayboxing a test level that I’m making, and I’m not sure how to go about doing the collision detection for the level. The level is being made with solid brushes (think Valve Hammer Editor) and I’m deleting faces that aren’t visible to the user.

However, this means that my terrain, which is modeled out of boxes, becomes paper-thin when I get rid of unused faces. If I recall correctly, colliders that are incredibly thin can be passed through when it comes to physics calculations.

What would be the best way to remidy this problem? Should I manually sculpt and add thick box colliders along the level (particularly the ground), use mesh colliders, etc? I know mesh colliders are available, but wouldn’t this problem still exist if I used them as well?

You can still model your own collider. When you put a MeshCollider component you will see on the inspector that basicly it just reuse your terrain model as collider. But you can change it to another model. So when you export your 3d model from your 3d app make also a collision one with the same pivot position. The collision model doesn’t need any texturing just export it as is it, then when you add the Mesh Collider component change the collision model to your custom one.