Few issues going on here – for one, zombies (and other creatures) have for quite some time now been able to see through cameras due to a change that happened sometime in the past 2-3 years, not sure which one. Back in early 0.C and late 0.B, cameras properly worked on-way. Basically LoS now assumes that if you can see them, they can see you, with no exception for things like cameras. Second, vehicles that are turning open up gaps in their walls, so to have a completely sealed vehicle you need at least two thick walls.
Currently, as long as you are not going directly n/e/s/w, any creature can enter your vehicle diagonally, shoot you, grab you, etc. There is no easy fix to this, aside from the workaround of making your vehicles have two layers of walls.
