I've felt like I've been moving backwards lately as I have returned to the parts I've not been happy with and started over.  Finally I'm at the stage where I can move forward again.
First picture, the Mk 2 electrics board.  I'm still using the Action Electronics 4 way switch installed under the cabin roof but have also added the two remote controlled relays to channels 5 & 6.  The nav lights and the cabin lights can therefore be switched on and off with two spare transmitter switches.  Everything else is switched with the 4 way.
Second picture, the Mk 3 sofa.  Slight flaw where the PVC isn't quite bonded to the backrest but there definitely won't be a Mk 4