North bound cameras have been noticed during congested traffic periods. There is one for each lane and they are located near the 6th fire extinguisher BEFORE the breakdown bay. I know this is a bit back-the-front but you'll figure it out with a few passes thru. The cameras seem to be mounted 2 or 3 lengths of galvanised pipe which run acrrosways. One camera for each lane. They are a dark grey colour.
The South bound ones are possibly about 300m into the tunnel in a similar style, but are harder to spot as one has less chance of going slow in a traffic jam this way.