Hi Nick,
I used some white protective foam stuff that you find in parcels :-) just stuck a load together with spray glue and used a hacksaw blade and some 80 to get it in to shape. I'm halfway through putting a coat of p40 on it to make it more solid now. Very easy to do and saved loads of time messing about with mesh / cardboard etc.
The door cards are going to have all hidden fixings. The whole door card as it's in a few pieces will screw together, its then hooked over the top of the door and hidden screws will be accessed behind the door speaker and through the door handle... that's the plan anyway :-)