Hummph. Took 2 hours out of the afternoon to work on the car. Needed to do quite a few jobs. First one was to fix the tunnel top down. Not the main part of it, just the front part (under the dash). To do this I have to remove the dash to be able to get the drill in there. Once this had been done, I now realise that the earth point under the dash gets in the way of the panel being fitted.
Tried to drill the first hole for the rivnut and realised that the drill is quite blunted. Rethought the plan and decided to rivet the panel in place, then fix the proper rivnuts when I can get to a mains drill.
To add insult to injury, the battery on the drill only lasted for the four holes. It looks crap, even the rivets don't look equally spaced :-(((

The seats also need a rethink. The mechanism for fitting them is going to have to be worked out really carefully or the whole thing will fail spectacularly, making quite large holes in the floor. It really needs a good ponder.
Seriously considering going back to the idea of the foam seats.