There is no way that Fraser would drive for such a long amount of time. He is familiar with the consequences of sleeping at the wheel, delayed reaction time and reliance on cruise control. The Dempster Highway has a particularly adverse camber (the road surface isn't level and drops away at the edges - extra bad with a high/heavy load, a raised point of gravity and a rammed gravel roadbed) and there are up to 13ft drops on the side to keep the surface above the permafrost.
General advice is not to bring a spare tyre, bring at least two. Remember that there are no emergency services and no manned stop-off points. Make sure you have enough gas/petrol/diesel and fill up some jerry cans before you depart. The surface is not secure, there is nothing holding the gravel surface down other than gravity. You could probably wreck a tyre or wreck the underside of your vehicle.
If you were a trucker under (illegal) pressure from your employer, you can probably do a 50h drive in four days. This, though, is based on a nice, flat, normal highway with nice weather conditions and a paved surface. I'm not sure how far you can drive on the Dempster in 13 hours, but I think halving it would be more than sane. Bringing a friend and driving shifts would be an even better idea provided you can sleep while bounced around on a load of gravel.
If I did take the 6 hours option, I'd be driving for five to seven days. It's easy to assume that Fraser [with drive times somewhere in between and broken up into shifts]* would never try to drive down unless he's carrying something too big or too heavy to fit on a Cessna or other 'bush plane' Fraser would probably only drive around his home ground (the northest part of the North West Territories) when he needs to get somewhere (getting medical emergency cases to the airfield, chase malfeasants) or he needs to obtain something (like shoot dinner).
The two hour flight from Inuvik to Yellowknife already sounded better than driving (you just need to realise that they're one a day, weather permitting) but it sounds even more attractive after you have considered the road journey. Before there was a full-distance road (the sporadically built Demptser Highway was, uh, sporadically built), your best and only option to get something large up there would be to put it on a boat.
So, if Grandfather Fraser bought a motor vehicle it would have been floated up the river. Interesting.
Also, another point supporting the idea that Fraser is not so much a bad driver than an inexperienced driver trying to navigate roads with 90 degree corners, large numbers of pedestrians and terrifying traffic density.
[possibly bfm: Fraser inherited his Grandfather's 1964 Landrover and spent two weeks driving it to Moose Jaw. It needed specialist parts [a 1960s big tractor/jeep cross imported from Great Britain... that would really take ages to get parts] and Fraser wants to upgrade and get a "snork" (snorkel attached to the engine so you can ford rivers without wrecking the engine) added. Since Moose Jaw was Fraser's first ever posting, he could have used up his entire vacation allowance before he even started and then road-tripped for two weeks. His commanding officer is not pleased and even less pleased when he sees the thing in the Detachment car park.]
[also poss bfm: Fraser has to explain that although his vehicle is older than Ray's GTO, it does not make him a classic car fan. Fraser is a practical vehicle fan.]
*Fraser makes claims upon micronapping - they were extremely facetious and passive-agressive.