For DEF, diesel exhaust fluid, my Chevy has about a 6,000 mile range per tank, so leaving with a full tank will get me to Fairbanks without a problem. I may buy a 2 1/2 gallon jug or close to that in Whitehorse as I will have used about that much by then. Shouldn't be a problem finding it on the trip. Just like fueling up, try to stay on the top half of your tank. DEF may be a bit more costly, just like the cost of fuel, but we are probably talking a couple of dollars a jug more. The quality will be the same, and check the dates on the product, just like you would here in the Lower 48.