Ok it didn't come when it was supposed to so I had to wait a week til I got a day off to go and collect it from the post office and fit it. It was a bit trickier than my last van so I took some pics as I was doing it for anyone else who may end up doing it.
With the seat out and base unbolted and tilted to one side, this is what the wiring looked like
About twice as much as my T5 and enough to cause problems making space for the safe. As well as the standard VW stuff mine also has some extra, rather mickey mouse looking wiring intalled by Westfalia icluding this
Google tells me this is a charger adapter. I hope to god it's just a control unit rather than actual charger for the leisure battery under the driver's seat as the wire coming out of it was on the thin side!
I had to unclip/unscrew all the relays and mounts that were attached to the seat base, remove all the cable ties and separate the bundles to route them up and out on the opposite side of the carpet cutout. I also had to cut part of the carpet away so that the wiring could come out in the right place to pass through the gap that they leave in the side of the safe base, without putting any pressure on them. Eventually looked like this.
Next step is to put the safe in, which uses the same mounts as the seat base. I connected all the wiring back up and tested everything to make sure I hadn't messed anything up before fastening the base down using shear nuts epoxyed to the mounts and red loctite in the threads, just to add that bit more awkwardness getting it out.
All that wiring will now not reach where it was originally mounted but there are plenty of suitables holes in various places on the seat base, so it wasn't difficult to find new mounting points for everything.
Then it was just a matter of taping the remaining wires down, plugging the seat heater cable back in and remounting the seat. I checked that nothing fouled when the seat moved fore and aft or swivelled and all was fine. The rear trim panel doesn't fit back on properly with a safe fitted, but I'll make some mounts for it that can let it sit about 40mm further backward and still unclip easily. It's going on the "when I get time" list
Then put my Heko deflectors on which was a nice and easy 2 min job thankfully