This weekend I fitted the redarc battery isolator. There is a sticky here on the topic, but essentially I took the positive lead off the second batt, and fed it into the isolator, then the rest as per instructions. It seems to be doing what its meant to. I need to source a 100amp fuse and fuse holder that will fit in the line, which is pretty thick (4G).
As others have noted, there are two captive nuts on the drivers side wall of the engine bay, which are lined up perfectly for the redarc, too easy!
Also begun to cut out some ply for the drawer system, but slides are a bit slow arriving.