Thank you all so much for your comments, likes and shares. I'm glad I persevered with this, I almost binned it at one point.
The Droid compartment: A TLC Build-a-droid astromech body already fit nicely into the existing socket on top of the vehicle, but I decided to put a lift in so it could pop-up into the socket. I cut out the side panels to put an access ramp. I have always found it frustrating when vehicles have hollow insides, but don't have any access to it (so I'm looking forward to getting TVC Troop Transporter).
The block part of the ramp is made from cut up pieces from a pack of disposable razors and packaging from some biscuits for the tread. This is also the access for the turret, you can just see the base that I put in for the turret.
There is a dividing panel between the droid compartment and the cockpit, which is made from plastic cut from a Christmas chocolate selection box and some more orange perspex.
Here's some WIP images of the droid lift: I cut out the shape for the droid from the existing enclosed socket, then added a cut out plastic lid (dark grey) to extend the shaft.
The vitamin tablet tube used for the lift droid holder, fit perfectly around the TLC-BAD droid body:
Next: The Turret Section...