How do they work and what's the line of sight for them look like, anyone able to post screenshots?

You can see the range of the camera here, this is taken from the official strategy guide.

https://www.metalgearspeedrunners.com/wiki/doku.php?id=metal_gear_ghost_babel:gbvr_sneaking_mode_no_weapon#sneaking_mode_no_weapon_level_6

How would this look when doing using the box, is there a visual for this, I do not know the actual size of snake's hitbox only guestimating based on videos

As for Stage 09, I look at the VR background for visual cues. The camera range (width) is larger than the camera itself.