Box colliders from procedural mesh

Hi all. I have searched and there are several questions similar to mine but I can’t find the answer I am looking for and I’m quite stuck.

What I have so far is a script that generates a mesh. Cross section of vertex a,b vertically and c,d horizontally like an upside down T in the x and y axis. And this is then repeated along the z axis to create basically a base with a wall in the centre.

I am able to generate and render the mesh as I want to and add a mesh collider, where collisions with a sphere seem to work when hitting the horizontal c,d plane but the sphere goes straight through the vertical one. It doesn’t seem to affect it at all, the sphere is not travelling fast (same at 50m/s and < 1m/s) and sphere is all scale 1.

From what I have read the problem is the mesh collider, however, I don’t understand why it’s fine for the horizontal but not vertical. But anyway, I understand it would be best to use box colliders for several reasons and don’t see a problem with doing so.

Instead of the mesh collider how can I create box colliders that are the same shape as the mesh from the vertices but say .1m thick (if necessary for decent collisions, thicker). I want to keep this so it is created procedurally as I plan to make like a winding base/wall along the floor and using two planes should keep it efficient.

I hope this make sense and is an appropriate question. Appreciate your time if you have read this, ta. (C# if it matters)

mesh.vertices = vertices;
yield WaitForSeconds (.05);
yield WaitForSeconds (.05);
yield WaitForSeconds (.05);