You will find that the inverter circuit is OK for a laptop as it runs up to 150w. As others have said, it's inefficient.
If you charge it while travelling, you will be fine. Too much off grid use and it will deplete the batteries. A solar panel will charge a laptop if you get a good one, or at least help.
If you are that much off grid, you will find that your fridge and lights are also consuming the juice, along with the roof, heater, and other little USB gizmos etc and in that respect, it's hardly worth making special arrangements for a low drain laptop, is it?
So drive daily, run the engine a bit, or take a spare battery or two, which you can charge on hook up.
I had loads of trouble trying to use the euro adapter socket - didn't want to spend £15 on an adapter when VW should have done it for us in the UK. So, as with Alan above, I made one from a £1.80 euro cable with a figure of eight end on it. Cut that off, and wired the end into a trailing socket I had. I then tried to find out on the forum how to know which way round to plug it in as it had live and negative with no reverse protection or earth. I then borrowed a tester plug, and put this into my trailing socket to find that it came up OK whichever way round it was plugged in, so the socket can work either way. This was mentioned to me by the electronic whizz kids on here, but of course it's hard to believe without satisfying yourself that you won't blow it up! The tester plug gave me that reassurance.
I now use it all the time, but remember to unplug the lead when not in use as it drains power from the inverter even with nothing plugged it.