Paco - 17 drums of fuel in the back of a Twin Otter?? Just about physically possible (I get about 20 empties in) but even with just 1 hour fuel in the tanks you would be at about 16 or 17,000 pounds (35% over MTOW). Twotter will take-off at that, but wouldn't like to plan to land it at those weights.
Wee Man - we used to go through Narsarsuaq quite often up till about 1999, they would not take any form of credit card, only cash US dollars. Don't know if that has changed, or if other Greenland airports are the same.