Well, haven't got round to the mirrors, yet. Did make a start on an under tray, but gave up as I got the choice of materials wrong - aluminium is very stiff and light, but hard to join so I'm going to try wood next. Much more green, and a lot cheaper.
I did manage to insulate the bonnet though:
using acoustic glassfibre, then filled in the frame of the bonnet with expanding foam:
Before trimming up, and refitting the original soundproof matting to hold it all in place.
Not very good pics. Engine heater gets off to a better start now, and car is warm much more quickly. I will try to measure temp against time with a domestic in/out thermometer at some point.
Unfortunately now that the engine is also very quiet, it is no longer drowning out all the rattles and whines from the rest of the car so I was freaking out a bit yesterday worrying about all the other things that might fall off, until I turned the stereo up.