Yes, I thought that might be what happened - but in any case I've checked with my mate now and neither his nor my phone had bluetooth switched on. Nor did we use the radio / sound system throughout the time.
Re the doors open scenario - yes, I too try to leave the doors and tailgate open as much as possible in these situations, as both the lights and the "Land Rover" screen switch off after a while (10 min? 15 min?), so I figure that must be when they stop drawing current. But when it's drizzly and showering on and off that is not always possible! I too, wondered about shutting the lights off and whether that shut down the screen & electronics - so it's good to know that this is not the case - thanks again Stig. Thanks also for the explanation re the alternator/generator set up.
Looks like the only answer is to avoid all unnecessary door opening, even if this means transferring more gear into the camper at the start of the period - or pick fine weather and just leave all required doors open! And pack solar panels and/or gen set just in case - but I guess 5 day camps are not that common either, so keep it in perspective. Certainly makes me grateful for the dual battery set up :)

