Hi Mick, I used 6mm (1/4") dynaliner which is probably the max. you could get away with. The rear wall trim doesn't quite sit as far back as it used to but has no ill effect, I.e. it's only me that would notice, it doesn't look wrong or anything. Back vents... When you switch the HVAC to recirc you can definitely notice the fan change and hear the extra air move so I guess it is slightly restrictive. It doesn't seem to effect the way it works though. I believe the speakers are much better, but it depends on your expectations. When you remove the OE speaker you'll see why even a tin can would sound better. One day I'll get around to replacing the front speakers as well, with some dynamat on the inside of the door and maybe one of those Focal self contained subs under the passengers seat. Roof trim is fiddly, not hard. Keep your hands clean. You need to remove the A pillar trims, sunvisors, clips, rear hooks, rear light, etc. The front light stays with the lining from memory.