Friction issue: pushing a box smoothly down multi-curved tunnel/chute

I won't explain why, but I need to push a [chamfer] box down tunnels/chutes like these:


with multiple bends, using real physics: RigidBody + meshcolliders - no motion paths. The object needs to be a box, too, although I'm using a chamfer box of course.

Currently my box bumps too hard and too often when the tunnel has more than one bend, but on simpler tunnels with only one bend I don't have any problems.

I'm using the same physics material on the box and the tunnel, it has Dynamic / Static Friction & Bounciness set to 0 and Friction / Bounce Combine set to Minimum.

The box fits inside snugly; I can't make it much smaller or it will start to rotate too much.

What Mass/Drag/Angular drag settings would be best for the box's RB?

I don't mind cheating physics as long as it looks plausible and doesn't use any motion paths. Should I manipulate Angular Velocity?

No gravity is used here BTW.