Why not set the exp data locations to a USB drive, but have two separate installations (app and charts) on the two machines? You can prove that they both work (inc with the instrument comms), but bring all your data across to the standby machine if the primary fails. To state the obvious: if you make the USB drive a single non-replicated component with key data (like Exp and the charts) on it you've not really got redundancy. USB drives fail too. Really key data, like polars and sail charts, I'd keep multiple backups of, on different media.

If I were your friend during  the trip I would then download any new charts, or Exp versions, onto a USB drive and install them onto at least the live laptop, but the USB drive would effectively provide you with the 'install media' and let you reinstall them onto either laptop. 

Thank you both.  I think the plan will be to install the software on both computers, so I can generate the 2 license keys.  Then backup the primary laptop to an external drive(s) .  If the one laptop fails the image can then be re-installed on the backup laptop.  The the license swapped.