WCollins,
I know he caters for a different sort of climate extremes but I think you could do worse than ringing Andy Bruce from Far North at Wick.
He can certainly help with giving you the name of the source for the fuel additive and I suspect a few more handy tips on how to tackle this trip too.
I take it that we can see a write up about this trip in a magazine near us shortly after the event!?!
FD